I did watch the film already knowing some big spoilers which I generally don't like to do but I really don't think that affected my viewing and reactions much.
Captain America was a jerk, Iron Man was a thug, the supporting character generally felt not as bad but were still pretty bad. The movie tried way too hard to make you side with Captain America but like all the heroes and just made them all look bad.
Captain America: Refuses to sign the Accords on the basis that the authorities might send the team where he thinks they shouldn't (which would prompt the obvious allowed choice of retiring) or not "let them" go where they should (which seems like something a lot more to even consider when it comes), not a whole lot other than the not-gone-into-again background experience with SHIELD to make him so averse to following authorities and insist they themselves are the safest and wisest. He refuses to make any compromise or surrender Bucky when it's clear he won't be killed, he chooses to ignore that or that even aside from that confinement of Wanda is still worth having a fight or feel that he needs Bucky on the mission (the other winter soldiers are so dangerous and shouldn't be found). He and Falcon decide that Tony won't trust the story or the authorities won't let him help-so it's best to not take a chance and try and just have Iron Man and others instead against them. Him considering and being tempted to kill rather than just wound Iron Man came out of nowhere and was a forced, cheap attempt to try to make the sides and blame more equal. Him responding to critique with some agreement by leaving the shield was interesting but it seems like he really only regrets not telling the truth about Bucky's assassination of the Starks and nothing else.
Iron Man: So much of the anger from the public, governments, Zemo feels misleadingly on the Avengers causing damage even though the damage was actually caused by the villains so it's pretty unfair. The movie and certainly the characters tries to avoid real wrongdoing and responsibility thereof, that during their most deadly encounter the Avengers were fighting a villain *that was created by Stark* (with him having the motivation that the world needed more security, regulation and surveillance and that power & control could be trusted and not abused). Additionally he confines Wanda despite seeming to not need to, he sides and works with Ross who believably Banner (who Stark was presented as close with) would have slammed strongly especially if he was still in and rising in government authority and later even thinks the Hulk would be on his side. The film deserves some credit for making his trying to kill Bucky, being mindcontrolled doesn't matter, pretty wrong but there's a little too much trying-to-be-likeable badass in his dialogue in the and, from how calm he is in talking with his computer system, not just or mostly just briefly rage-driven and not a lot of likelihood he will later feel regret. By the way what was his father doing with 5 patches of super soldier material?
Black Widow: Scarlett Johansson plays her pretty well with and improves what she has but. She initially has a believable change of position to supporting the Accords, it's uncomfortable but I guess believable that she is so not admitting of doubt or regret or unfair circumstances about doing so with T'Challa. The big problem is when she declares Steve doing anything for Bucky is Making Things Worse and in response to him pointing out that Bucky is alive and otherwise wouldn't just shifts to wisecrack that he breaks stuff and that his shield is government property. Then she, after Ross confirms that Bucky would have otherwise been killed and with time limited, suggests she and Iron Man team up with Black Panther who earlier told her he would kill Bucky. Then when she helps the escape she says she would help Black Panther find not catch them, ignoring the initial and present possibility/probability (what the conflict was generally about) that he would kill Bucky (maybe this was diplomacy but avoiding it for what she does say sure is awkward). She does rightfully slam Tony for being more upset about *changing sides* then considering that they might have been wrong but then she, on being warned, oddly, awkwardly, even stupidly claims that he rather than she should watch their back.
Scarlet Witch: Probably the worst non-protagonist character. Initially feeling guilty, so much that she's a toss-up about signing the Accords, and so not really needing to be confined but being so anyway, on being presented with the opportunity to escape says she's done enough problems, then on Barton saying joining him and Captain America is how to redeem herself decides it doesn't matter how others feel about her just that she doesn't fear herself and later tells Barton to not pull his punches in battle against the colleagues. Her story ends with Vision saying he's sorry what happened to her but that things did turn out, from what she did, as he had said they would.
Barton: A close contender. He backs Captain America because he feels he owes a debt, nothing about why there is so much more for him and not Iron Man or care that Natasha supported the other position or yeah, why he cared so much about Captain America over his family life to support the illegal side (other than yeah I guess kind of believable belief that he wouldn't suffer consequences, at least not as bad as separation from his family when Iron Man leads the other faction, but that's more not really believable).
Spider-Man: The portrayal could have been worse, it was better than my rock-bottom expectations but. He has an OK initial introduction as Peter (coerced to fight though he becomes convinced, unseen, during the travel time, a bit undermined as inept already but not too much that Stark somehow knew his identity) and the beginning of the big fight, initially respectful with Captain America and the banter is overdone but understandable, then the filmmakers try way too hard with the humor hurting the character. His initial motivation is weak but understandable, somehow crazily accepting Stark's claim that he's for the little guy and presumably that the UN should have authority (thankfully the film kind of but vaguely suggests it's only for the Avengers, he isn't trying to make himself subservient which almost seems hypocritical or if he actually is, who knows), then gets worse by the humor. He presumably would back the Iron Man side because he told him they were protecting a mass murderer but that is undermined his Awesome at Winter Soldier's metal arm and he especially comes off as pretty idiot with his classification of The Empire Strikes Back (it's really old and adults may not have seen it) and being (without any specific previous details for context) indifferent to Captain America's claim that the situation is complex and he's the good guy, thinking that just makes him dangerous and not considering that that could be the case for Iron Man. In the end he seems fairly bitter at Steve but there's some hope, at least there can/could be, that he's moving away from Stark (though it's slim hope) and may have decided he should be more independent and improve himself.
Ant-Man: Supports Captain America's side just due to his personal esteem for Captain America with nothing for why he doesn't have comparable or at least substantial esteem for Iron Man (well he does find out Iron Man is the opponent just before the fight). The film lulz that as a former criminal he's OK or eager to break the law, no big deal, really not care about his family his own film presented him as devoted to and thus (more or less) really regretting his criminal past and appreciating his hero opportunity. He almost comes off, as Spider-Man sort of does, as someone tricked into fighting but then he's far too passionate and intense in some of the later fighting.
Secretary Ross: A very dishonestly portrayed character. He initially admits the world owes an unpayable debt the Avengers and within a minute shows he really has hostility and no gratitude. He comes off villainous but nowhere near what he previously was shown to be in TIH, not indicating clearly there's really been a change or reason for it (the heart attack possible but unlikely as it's tied with his opening contradiction and he comes to show he actually still is about as ruthless if not quite as unreasonable).
King T'Chaka: Saying that the supposed protectors of people are actually indifferent to innocent people is rather offputting hyperbole but realistic enough and not too blatantly misleading.
Black Panther: OK. The dichotomy of his father and him as a leader being strongly against unauthorizd vigilantism but him doing so and other characters not liking it but having to be pretty accepting of it because he was a sovereign was interesting. He did change his mind at about the right time and for right, believable reasons but him therefore going away, not trying to dissuade Tony though he felt vengeance was consuming the fighters (which it didn't seem to be Steve until it almost did), was pretty questionable, him finding Zemo a little forced but interesting interactions with him, sharing grief but ultimately thinking there should still be justice including capturing him. His claim later that he was helping Bucky find peace when it was close to the death he had always wanted felt overly poetic if not pretty self-serving but OK.
Vision: Decent, the worst thing about him was mainly that other characters (especially Scarlet Witch and Captain America) didn't do as he advised or even seem to consider or take it much into account. But it was forced and cheap that as powerful as he was he couldn't harmlessly knock out or remove Barton or stop War Machine harmlessly or with a lot less force and the latter is awkwardly just waived that he was distracted.
War Machine: Initially lauds Ross because he received a Medal of Honor and condemns Captain America as a criminal after a sequence in which (though I guess this is the audience knowing more than the character) he was more or less very clearly the good and reasonable guy. In the end still backs the Accords, despite or including the consequence that his colleagues are in super-max prison and that they were trying to prevent a real plot and most of the conflict that led them there manufactured-and then admits despite the support despite the circumstances he's not sure if he hasn't changed his mind that supporting the agreement was right. Then when Steve reveals to Tony he broke the prisoners free and they'll operate on their own it's like his opinion doesn't matter.
Sharon Carter: Captain America's conscience, probably maybe. She uses her aunt's feminist grounding applied to tenacity in general (and specifically for sticking to individual judgment even if the whole world is against even though it was also about succeeding in hierarchical organization and law enforcement as she was also doing and is proud to) to inspire Steve, intentionally or not, then, then tells there will be shooting-to-kill as if it's unfortunate but understandable/pretty unavoidable, not that exceptional, then gives Steve more and more help.
Winter Soldier: Very random how much he knows about Steve when, how to get him out of mind-control. Very childish to have the prologue and so many other scenes (like fighting masses of cops with continued minimal defensive force) emphasizing that he's innocent and not harmful, only mindcontrolled, no doubt for the audience and so also more-right protagonist Steve (and later we find that Zemo, despite having gotten the activation words, didnt even initially mind-control him to do the bombing, just somehow framed him). For him to at the end after all the loss and sacrifice to "go back under," not far from death let alone the maybe imprisonment his friends and the film were opposing, made the whole film seem more superfluous. Also why did the other winter soldiers revolt and he didn't, or did they?
Zemo: Pretty so-so, interesting schemes and maneuvers (and kind of that he was not for Hydra though using their methods and techniques) though questionable he could be so successful, especially from just a year of study, but it was a nice, surprising but believable touch that at the end he quickly went for his gun not to try to kill Black Panther but himself.
