The Kingdoms of Amalur: Reckoning demo, yes I only played it because of the Mass Effect 3 items, but that's what forms the majority of this story.
First time I played it I was vaguely impressed. It was sort of a more serious Fable, the world seemed interesting for a rather standard fantasy fare, but then as I was speaking to the first Fateweaver, conversations just disappeared with a lovely bug. However, there was a prize at the end of the road so I pushed on, ran across the play area to see as much of the main quest as I could to see if it grabbed me. It sort of did. But then it happened. It crashed. One of those big ones that freezes the entire Xbox and the only way around it is the power button.
Any other game would have gotten a “Well that's buggy as week old shit” and forgotten, but there was a Mass Effect unlock waiting at the other side. A few days later I had another pop. I had a few hours before I had to head out and figured I had plenty of time to fit in the 45 minutes needed. This was when I realised just how amazing a demo the game was. First I didn't have to redo the tutorial the game just went “Shall I skip that part since you've done it already”, which I thought was going to be the most painful of the replay. That done I set off handling the quests I'd blatantly ignored previously and I was in for another shock. The disappearing conversations were nowhere to be found, and I'd never see them again.