Driver SF: I didn't want it at first, got it in a Steam sale and it turned out to be one the more enjoyable arcade racers last gen.
Bioshock 2: After I finally played it on ps+ it's now my favorite in the series in terms of level design.

Most recently: Hotline Miami. I noticed quite a few posters praising it and calling it their GOTY and I kept thinking, no way a game with such terrible graphics. Not saying that graphics = quality but I am tired of all the indie titles with the old 8bit graphics. Anyway, bought it for around £2.50 and by no means regretted my decision. I still don't think it's all that, but the gameplay is really something impressive which makes the game incredibly addictive and equally frustrating.

Dark Souls.

Metroid Prime.

When I first played it, I loved the intro, but once I landed on Tallon IV I found it tedious, frustrating, and confusing.

Going back and playing it years later, I now consider it one of the greatest games I have ever played.

Forza...as a series in general, but mainly it was Forza 3 that changed my mind. After how meh GT5 was...and me becoming more of a 360 guy I played a lot more Forza 3 and quite enjoyed it.

Final Fantasy VII, although I used to hate on it before playing it at all.

Halo. This was back before they remade the controller though. I was worried a new console maker would push someone out, like with Sega. It was unjustified and I loved halo 2. But that controller did suck.

I didn't enjoy Pokemon mystery dungeon the first time I played it, but after playing Diamond I decided to come back, and it sure was worth it! The same can be said for Pokemon Rangers actually.

Also, SM3DW sort of should be counted here, although I liked it from the get go the first trailers were beyond disappointing.

Not as much individual titles, but for me, two franchises come to mind.

LittleBigPlanet: When I first saw trailers and gameplay videos for the first game, I thought the characters looked ugly, the gameplay looked floaty and annoying, and couldn't quite figure out why a game like that was being so heavily bundled with the PS3. Well, a friend of mine put in one of the games at a party some time ago, and I couldn't believe how much fun it was. We played it for hours, just trying out different customized levels people had posted. I loved the randomness of it; playing Indiana Jones themed levels, a weird Japanese Titanic reenactment, to a ~5 second game where the only point seemed to be to not get killed by a billion sharks coming out of nowhere. I can't vouch for how it is single-player, but the game is perfect for parties. For us, it joined the ranks of Mario Kart, Crash Bash, and Super Smash Bros in creating that non-stop chaotic fun that everyone can enjoy.

Pokemon: I loved this game when I was a kid, but got tired of it come 3rd gen. The whole thing seemed so repetitive, just going from Route to Route collecting enough Pokemon to beat whatever element-themed gym you had coming up. Not sure what changed exactly, but my sister convinced me to try out Pokemon Conquest on the DS, since I love strategy RPGs, and I found myself really enjoying the collection and evolution aspect of the game. Admittedly, Conquest is a lot different than traditional Pokemon, but I still thought I'd keep an eye out for the next one, and see if it had enough to bring back an old fan like me.

Well, I got Y version for Christmas, and I absolutely love it so far. The formula feels fresh, while still keeping the same basic elements intact. I'm enjoying reliving what I loved about the old games, while enjoying the new additions at the same time. In particular, I like how the game really just throws you into the thick of it, and figure out for yourself how to master training and battling with your team. I feel bad I gave up on the series for so long, but I'm happy I came back. The games really deserve the acclaim they get.

Red Dead Redemption and MGS4.. now they are in my top 10, yeah i was an idiot.