Games like Super Mario Galaxy, BioShock, The Last of Us, Mass Effect, Skyrim and Assassin's Creed 2 had all the hype in the world (high profile studios and/or series).

Games that really surprised me were titles like The Puppeteer, Resogun, Mirror's Edge, Darksiders, Overlord, Portal, Guacamelee!, Journey, Ghost Trick, Trine, World of Goo, Venetica, Braid and Hotel Dusk: Room 215.

Project Gotham Racing 3
Grand Theft Auto IV
Red Dead Redemption
Need for Speed Shift
L.A. Noire
Forza Horizon

Some games can have a lot of hype, but still be able to surprise you with their awesomeness. I remember GTA IV surprised me a lot with the tech and details. And I already knew it had received a lot of 10s and it was the most expensive game in history. It was really remarkable.

Super Mario Galaxy, Super Smash Bros. Brawl. Legend Of Zelda Twilight Princess & Wolfenstein the New Order. (PSYCHED)

Skyrim, Red Dead Redemption, Mass Effect.

Call of Juarez bound in blood and sleeping dogs.

-Uncharted 1 and Uncharted 2- cause I didn't expect Uncharted to become my 2nd favourite series of all time.
-TLoU- cause I didn't expect to like it as much as Uncharted 2.
-Bioshock infinite- cause I didn't even wanted the game.Played it this year through ps+
-Dark Souls- I wanted the game but I was hesitant.Then i found it for 20 euros, 4 months after release.
Souls series is now my 3rd fav series.
-Little Big Planet- It was bundled with my ps3.The most fun game I've ever played.

You might think,How the hell was I surprised with games that were all like 90+ on metacritic.
Well, I've played many 90+ games. I really liked most of them but when a game ends up getting in my all time favs list,then I am surprised.

Assassins Creed 2
Halo 3: ODST
Homefront
Forza Horizon

Mass Effect 2/3 and The Wealking Dead: Season 1

The picks in this thread so far are disappointing... for me only 4 games hooked me in during the 7th gen.

Uncharted 2
Demon soul's
Wipeout HD/Fury and
Vanquish. 

and in the 8th gen so far, The last of Us (i skipped it in the 7th)