Borderlands - I was psyched for this. The concept was awesome. The trailers were incredible. The guns shot lightning. It was going to be super magic co-op multiplayer happy fun times. Unfortunately the single player is fairly repetitive, and the multiplayer is criminally flawed for it's lack of basic loot distribution systems, server browsers, etc. Especially for the PC - ugly console port fingerprints abound. I really do believe that this could have been huge, but Gearbox just couldn't deliver on the details to realize that potential.
Oblivion - I was really hoping to like this one. There're a lot of borderline parts to the game that brought it down for me: weak central plot, stilted/eerie NPC conversations, repetitive dungeons. The straw that broke my back was the fatal combination of the unintuitive skill-based leveling system and auto-scaling monsters. So I spend two levels working on lockpicking, stealth, and alchemy and now everything's pounding me into the ground?! Not cool.
Far Cry 2 - Far Cry had no story, but it was awesome. I loved it. Beautiful before its time, and a solid shooter. Far Cry 2 promised an even more open world, more of a story, player choice, enhanced environmental/vehicle effects, etc. It should have been great. It wasn't. The unskippable railroad intro sucked. The illusion of player choice sucked. The missions sucked. The voice acting was horrendous. But particularly, the driving S U C K E D. I couldn't STAND having to spend so much time driving from one side of the map to the other with one eye on the map and the other eye on the Hummer chasing me. Total fail. And why did they even put the Far Cry name on it? No connection to the first.