I thought that the bodysuit and scales worked much much better in the movie than I anticipated - and I pretty much cringed every single time I saw a Mystique still.
Characterisation though I was not really satisfied with. It's like, Mystique is the character whose actions change the world, but the movie mostly treats her like an ass-kicking rogue missile that needs to be stopped, with very few humanising touches or insights into the character and her motivations. I thought her character suffered from the 10-year-skip the most - at least with Charles and Erik we got some background information to fill in the gap, but for Mystique there's literally nothing, except Erik's words that she was "strong" the last time he saw her. What did she do for the last 10 years? Did she split from the group right after Erik was captured? What was she doing in Vietnam? Was she already tracking Trask by that point? Was she trying to find out what happened to her Brotherhood friends? When she finds the autopsy photos in Trask's office, was that meant to be a big turning point when she really decides to go after Trask? If so it didn't really come across that way to me - from what I could see Mystique was already mighty angry and determined even before she finds them, so I can't say that moment felt particularly significant.
Also, at the start of the movie old!Charles makes a big deal of the fact that Trask was Mystique's first kill, and that she truly became Mystique on the day she murdered him. That crossing of the line when Raven really loses her soul could have been interesting to explore, except that the Mystique we see in the film seems to be totally onboard with killing already, with no moral qualms or hesitations in sight, ready to choke Stryker (?) to death in the very fist scene she appears in. If anything I found it hard to believe that Trask was going to be her first kill.
I can't say I'm very clear on Mystique's actions and motivations at the end either. When Erik tells her that he tried to kill her because her blood was going to doom them all, why doesn't she go, "um what blood what on earth are you talking about?" Does she already know everything about her DNA, the Sentinels and the dark future at this point? How? Supposing that Charles somehow manages to explain all of this to her in the brief time before Erik tries to kill her, why does she appear not to give a slightest damn and just keeps repeating that Trask is the enemy? Why, in the airport scene, does Charles keep appealing to her better nature and never to the fact that her actions might doom the entire mutant race? Why does she herself not seem to care about that fact until the very end, when she suddenly gets convinced that not killing Trask would be really great PR for the mutants? I don't know, maybe the movie was meant to show her so obsessed with Trask's death that she's blinded to everything else, but if so it wasn't well executed at all and just made her character look all muddled. Even that pivotal moment in the end when Mystique decides not to kill Trask is not really about her - it's really all about Charles and his decision to give Mystique a choice.