Well, I can think of a few:
Command and Conquer: Generals
Yeah...no. Thing is, I actually enjoy the Generals sub-series for its gameplay, but in terms of content? We had the Tiberium series (sci-fi, near to far future, serious storyline), Red Alert (pulp sci-fi/red scare, hammy storyline) to...this. USA, China, and GLA, a.k.a. "the terrorist faction" whose motives are...kill Westerners and Chinese? Yeah, the story's pathetic, the characters are non-existent, and for a series that always had a strong worldbuilding component, this just came off as generic. Fun to play, but the Generals setting is easily my least favorite of the CnC settings.
Gears of War: Judgement
Ask GoW fans which is the weakest game of the series and Judgement will usually get nominated. And personally, I heartilly agree. Again, it's not a bad game, and it does add new weapons and enemies, but something about Judgement feels...off, compared to the other games. I know it had a different developer, but apart from that...it's hard to say. But it felt unnecessary from a story standpoint, and...I dunno. Gears is a weird mix of over the top (chainsawing enemies) and under the top (melencholia as one wanders through the ruins of human civilization), and that's not even diving into its EU. But Judgement felt less like a Gears game, and more like a cover shooter with the Gears logo slapped onto it.
Doom II: Hell on Earth
Oh boy, this is going to cost me. But yes, I do think Doom II does meet the definition of generic, taken in the context of its predecessor. But first, I think I need to give some context. I do like Doom at the end of the day. I rag on it a lot, I consider Marathon the superior version of this shooter in a lot of ways (more story, dual-weilding, reloading, the survival aspects, etc.), but Doom does win out in the end. I played Doom back in the day, but only fully completed it with the BFG edition. So, that was fun, I thought, let's try the sequel.
It's the same. The exact same. Oh sure, you get a new demon here, a new weapon there, but it's the same. Damn. Game. And, IMO, weaker than the first. It doesn't have the same sense of progression that Doom did, where Phobos, Deimos, and Hell all had their own feel. No, we have spaceport, city blocks, and Hell. Doom II seems to be going for more realism than Doom I, and I've heard it speculated that a lot of Hall's old designs were recycled for the game, hence the disconnect in look. Oh, and the story's still bollocks. Yes, Doom I didn't have much of a story either, but I can at least give it credit for storytelling techniques (e.g. the environmental design of Deimos). Here, while Doom II adds material, it feels less tightly designed, less interesting, and for me, a chore to play through. Games get flak today for recycling concepts, but this is one of the worst cases of recycling I've seen. And even for the era, I can't help but think of the jump between STH 1 & 2, and all the advances that carried with it. I can't help but compare Marathon: Durandal to Marathon, which, while I enjoy the former more, the latter at least provided a new setting, continued the story, and provided new weapons as well. What can I call Doom II bar more of the same?
There's probably others, but I guess by definition, something that's generic isn't going to stick out in your mind much.