Definitely Fallout 3, I hated it for ages. I tried on two seperate occasions to play it, weeks apart, putting in a couple of hours each time. I just couldn't figure out what the hell was going on, what I was supposed to do, etc. I blamed the game, and deeply regretted buying it. Then, one day months later I saw it sitting there on my shelf and I thought; I payed damn good money for that, and I suppose if nothing else, there's achievements to be had. So I popped it into the drive that third time, and the next thing I knew, the time was 2am. After that, I didn't play any other game for ages. Today it and all five DLCs sit on my 360's hard drive, having contributed its full 1,550 gamerscore to my total. Roll on New Vegas.