Valeris (SPOILER)
I'm not sure whether I need a 'SPOLIER' for a film this old, but I've seen other posters criticised for 'spoiling' less (i.e. for giving away plot points of even older films) so I'll be cautious...
Anyway, it bugs me that Valeris, a seemingly strong female character who was the first Vulcan to graduate at the top of her class at Starfleet Academy, turned out to be an evil traitor. Must intelligent, capable women always be exposed in these films to be deeply 'flawed'? Is this the message we want to send to young women (i.e. if you study hard and become the top of your class chances are you're an evil beetch)? Not smart.