In other words what game surprised you the most when you bought it.  A game that you got and didn't expect much from  or just bought  because you were bored, but after you played it the game was amazing to you.

For me it would be Wipeout HD.

Ooh, WipEout HD is a great game! ^_^

Mine would probably be Lego Star Wars. Yes, Lego Star Wars. I was really bored, at walmart, and I had $60 in my pocket (plus tax). I saw it and thought, why not? I like legos, and Star Wars, so I'll give it a shot. Turns out, its a lot of fun, there's good humor and it's great to play with a friend.

Grid.

Wanted a racing game, saw some of it's ads, heard a few minor things about it, tried the demo, played the same track over and over, bought the full game off a friend, played it over and over.

Didn't expect to end up likin it this much =l

Eledees/Elebits

The Simpsons Game. My 7 year old picked it out and I said to myself "Meh. Why not". About 30 minutes in, I was hooked! Wish I'd have bought it at $60!!

Probably killzone2. I thought that killzone 1 was mediocre, so I didn't expect anything from the sequel, but well, after playing the demo, I knew that guerilla would give us a nice game.

Lost Odyssey

Picked it up because I needed a JRPG fix (but the grinding in Enchant Arm had turned me off to JRPGs a bit...), then couldn't tear away from it for like 2 months.

No More Heroes.

The Darkness. I didn't really expect much out of some FPS (I'm not a big fan of the genre), but it was a lot of fun and the story was pretty amazing.