Resident Evil 5:
Albert Wesker: When I played the earlier Resident Evil titles, I liked Albert Wesker. I didn't know why he did the things he did, but he sure did them with style. Boy was I disappointed when in Resident Evil 5 he just turned out to be some generic misanthrope. Seriously Wesker? You've accumulated all this power, and this is what you do with it? And you're going to talk to me about natural selection like I'm a 4th grader the entire time we fight? 2/10, would not replay.
StarCraft II:
Arcturus Mengsk: I had thought that getting to take a closer look at his Dominion would be an interesting experience, but it turned out to be rather generic as far as dictatorships go. Blizzard didn't opt for a lot of subtlety in the environmental storytelling when trumpeting their "MENGSK IS EVUUUUL!" message. When playing the first StarCraft, I thought Mengsk would be above using those corny holo-billboards Raynor destroyed on Mar Sara.
Infested Kerrigan: Kerrigan really was a delight in StarCraft. She was cunning, funny, brutal, and she seemed to take so much joy in taking her enemies out of play. Not in StarCraft II, then she lost her sense of humor, stopped killing important people, and just spouted fatalistic nonsense every time she and Raynor met.
The Overmind: I seriously hope that Tassadar was lying when he said that The Overmind was just misunderstood. Before StarCraft II, we were to understand that he was originally a tool of the Xel Naga until he grew tired of taking their orders and freed himself. Now we're to understand that he was a victim all along. Lame.
Metroid Other M:
Adam Malkovich: After playing Metroid Fusion, I'm not sure what I was expecting, but wow, this guy is as boring as paint.
Samus Aran: I'm sure you've already heard about how Other M ruined Samus ad nauseum, so I'm not going to bother.
Mass Effect 3:
The Geth: I felt that in Mass Effect 3, they sacrificed everything that made their race unique and interesting. By having them use reaper code to survive the Quarian onslaught, not only did they sacrifice their distributed intelligence, which made them one of the few races in Mass Effect that felt truly alien, they abandoned their conviction that by accepting the technology of others, you blind yourself to the alternatives.
Donald Udina: Seriously? What sane reason did this guy have to collaborate with Cerberus, is BioWare saying that if any character doesn't like Shepard, they must be insane? I like having to deal with characters who are opposed to your character in RPGs who you aren't necessarily supposed to murder, makes it feel like a bit more than a simple power fantasy.
The Reapers: I don't know what I expected their motivation to be, but I was hoping it would be something that makes a bit more sense than murdering trillions of organic lifeforms every 50,000 years to save them from being wiped out by other synthetic lifeforms. Hell, even if they let you beat the game without discovering why the Reapers did what they did, it still would have been better than this.