I think how good or bad the costume for a comic character looks is highly subjective and accuracy does not always mean the costume is "good" since plenty of comicbook costumes are inherently bad and won't look nice on film. For eg. I love Olivia's costume though there will be people who don't like the costume.
The thing with every costume though is, it should be identifiable. If I see a character in costume I know nothing about I should be able to identify him from a lineup of comic iterations. For eg. For all the gripes people have with X-Men costumes if you see Anna Paquin in costume you can tell it's Rogue. The essentials in the character are intact. Unfortunately, Apocalypse, for me, fails this test. Now we could argue that the iteration they went with is good or whatever but since he is a major character whose appearance is sort of iconic in the way Darkseid or Galactus's look is iconic I still can't get past that right now.
Yeah, I agree you should at least be able to tell who the character is. Some costumes (such as many of the X-Men costumes) are ones that I don't think would translate straight to live action, but the live-action characters should at least resemble who they are supposed to be.
Even going by the original 2000 X-Men film, if I look at Wolverine, Xavier, Cyclops, Magneto, Storm, Jean Grey, etc., I feel they pass that test. If you showed me a photo of those characters in their film costumes, I could easily tell you who they were supposed to be.
For an example that would fail the test, we can look at the Fantastic Four remake. If you showed me a photo of Mr. Fantastic, Invisible Woman, Human Torch, Dr. Doom, and Mole Man from that film, I doubt I would be able to name any of them if you didn't tell me who they were supposed to be. The lone exception is The Thing. That's a complete across the board failure in costuming and character design.
I'm not going to push for complete adherence to the comics, but we at least need to be able to tell who these characters are at a glance. It is important even for non-comic films that characters should be instantly recognizable. Characters like Darth Vader, James Bond, Indiana Jones, The Man with No Name, etc. are iconic at least in part because of their look.