Dragon Age: Origins - Good lord. Now, I actually love this game after repeat playthroughs, and no longer feel the length like I did the first time... but the first time was absolute murder. It seemed like every idiot with a lyrium addiction had a labyrinth under his home you had to traverse to take him down.
Final Fantasy XII - Another one I love, but I always feel the length on this one. In Final Fantasy X, around the 30 hour mark I'm just about finished with the game. At that same point in XII, I'm only just wrapping up the first act. The unfortunate part of this mess is that the first and third acts are great, while the second should be about 5 hours of gameplay, but is extended to about 40 if you do side quests. What. The. Hell.
Black and White - I've probably started this game 10 or more times, but only beaten it once.
The Elder Scrolls - All of them. I know, that's the idea, right? However, I seem to get burned out on these games way too quickly between interesting moments. Let's hope Skyrim can keep interest up as well as Fallout 3 did.