Okami

just playing it now and i can't believe how great this game is

It wasn't terrible but after the absolutely incredible Super Mario World 1 it was a massive let down!! None of the magic I loved from SMW1 was captured in Yoshi's Island. 

Persona 4: Golden
I was hyped for this, and I was expecting a good game. But I wasn't expecting it to be THIS good. Many of the aspects of the game I thought I wouldn't like I ended up loving.

Final Fantasy VII
This is probably my easiest answer. I bought it at a boot fair with my step brother (first time meeting him) because it was 20p. I really wasn't expecting much, in fact I was expecting it to be POOR. But the next day I was hooked, and a few weeks later it became my favourite game of all time.

Tales of Vesperia
Similar story to Persona 4: Golden. I was hyped, I was expecting a good game and I spent a lot of money on it, but it still managed to greatly exceed my expectations. Possibly my favourite game of this generation.

Fallout 3
It was an impulse buy. I had recently gotten a PS3 and all my other friends had bought the game too. It also ended up being one of my favourite games of the generation.

Skyrim
I bought the game because it was cheap, I had pretty low expectations after playing Oblivion. On the 2nd day of playing I ended up logging 12 hours. Yeah, it was that good!

Heavy Rain and Fallout 3 in this gen.

also i think the tittle should be "didn't expect to blow you away"

i didn't expect xenoblade to be my favorite RPG this gen

journey..had me crying at the end

Valkyria Chronicles, The Walking Dead and to a lesser extent Call of Duty 4.

VC is just a brilliant, fantastic game. Game of the Generation. Brought a tear to my eye, too.

TWD. Amazing game. Seriously. Game of the Year 2012. Brought 2 tears to my eyes.

Call of Duty 4. Blew me away. Got addicted. Wasted 2 Years of my life on the game. Brought a tear to my penis.

Demon Soul's. I remember watching my friend play it, and I said "why would you want to play something that makes you die over and over like that?"

Wish I could go back and slap myself in the face. Ignorant comment, because the series has transformed into one of my all time favorites.

Most recently, last year's SSX. I love the series, but after the reviews + On Tour, I didn't have high hopes. But I genuinely loved it aside from a few minor niggles.

Team Fortress 2. I dunno what I was expecting from it, really. It was the least appealing part of The Orange Box, yet actually ended up being my favourite.

Pikmin. Came free with my Gamecube; became one of my favourite games of all time.