NOTE: The following game is a game I still loved, but in comparison to its predecessor, it could have done much, much better.
Fallout: New Vegas
Fuck the glitches, that was not the game's biggest issue for me. What I hated was that the side quests were so boring and uninspired. They usually consisted of "talk to this guy, then talk to that guy, then go here, then go back to the first guy for reward." There was no interesting back story to it, it was just "this guy wants that, so go get it for him." Sure, maybe they gave the quest a little story, but they were so forgettable that I couldn't remember what they were an hour after I finished them. Now, sure, there were a few good side quests here and there, and the companion side quests were really engaging. But that's only a few compared to so many bad and forgettable quests. They felt like chores than actual quests.
But quests don't matter as long as you have an immersive and engaging world, right? Well, that was another problem for me: The world didn't seem as alive as it did in Fallout 3. In Fallout 3, nearly every little area had a little story behind it. Sometimes it was an epic goose chase for a cache of loot and a story found through holo-tapes, sometimes it was just a couple of skeletons in a bed, living their last moments together before the bombs fell. I found almost none of that in New Vegas. There weren't any interesting characters to talk to, there weren't any stories that made me interested in the world. It was just boring. Plain little obstacles to get me some to some loot. Sure, Fallout 3 did that a bit, but not as flagrantly as New Vegas.
Another little side note that may be a little nit picking, but I feel is necessary to mention: Half the voice acting class seemed bored out of their minds. I'm not talking about the companions or the main characters. I'm talking about the voices that you'll hear again, and again, and again. People said the cast was better in New Vegas. I argue otherwise.
Now, before you get your panties in a bundle, I'd like to say this: There were a lot of things that New Vegas did right. The main quest was fantastic, fooling you into thinking that it was a simple search for revenge story, only to find out there were bigger things at hand [small](though, it was kind of obvious that it wasn't just a goose chase story. More would have had to happen)[/small]. It gave you much more freedom and control of how you want New Vegas to be ruled. I like Fallout 3's main story, but New Vegas took the cake with that.
So, yeah, I thought New Vegas wasn't as good as Fallout 3, but it still had redeemable qualities. Still a let down, though.