This thread has been done at least a half-dozen times, but, yes, I know the search bar is broken.
Anyways, OT:
TES4 - Oblivion: It was thematically less rich than Morrowind, its predecessor, in that the world was not very convincing, there were less factions and less inter-faction conflict which really made Morrowind intriguing and deep. Also, the art design was very generic, all variations of western medieval settings - stone and thatch everywhere. In addition, leveling/difficulty was broken, a lot of my favourite spells were taken out, the wildlife was boring, too much shiny shiny bloom effects, and the main quest was difficult to relate to. I lost faith in Bethesda until Fallout 3 was released.
Borderlands and Hellgate: London: Borderlands was better than H:L, let's get that clear first. H:L had significant combat problems which Borderlands didn't, such as poor recoil response leading to the feeling that you were shooting off paper-clips. But what really sucked for both games is that they emphasized the wrong parts of the RPG genre, it was all loot and leveling, no actual story, characters, or decisions. I quit both after a while because I couldn't give a damn about the world enough to continue playing. Hugely disappointing, I'm still waiting for a good FPS/RPG along the lines of Vampires: the Masquerade Bloodlines, which is the only success in that hybrid genre so far, and even that title has its flaws.
GTA4: Horrible performance on my PC and that crap with the 'friends' constantly calling you. Also, they decided to keep the outdated save game system which should have been abandoned years ago, but that wasn't really a factor in my disappointment.
