Mario Kart Wii - Had high hopes, but it greatly surpassed them
Trauma Center: New Blood - Who knew surgery could be so fun?
Excite Truck - Only got it because it was a launch title, but had a super blast with my friends
Professor Layton and the Curious Village - Engaging yet frustrating puzzles and a very likable title character
TellTale's The Walking Dead - I expected action, not huge emotional engagement and crying. Even better

8th Gen:
Divinity: Original Sin - Left-field game my friend suggested, we've been having a ball with the customization and open-worldness of the whole thing. Definitely try it out.

If these games had hype, I wasn't aware of it.

Crackdown
Mass Effect
Condemned
Sonic All Stars Racing
Tales of Vesperia
Oblivion (my first in the series)
Phantom Breaker: Battleground

Batman Arkham Asylum, went into it not expecting much, but I heard good things and I never played a Batman game and I was like what the hell, wow was I blown away.

Xenoblade (Dat gameplay and story *.*)
Mass Effect (wasn't really interested in this game but as i played it, i got totally hooked)
Super Mario Galaxy - no explanation needed

Oblivion/Skyrim , Mario 3D World , A Link between Worlds, Goldeneye Wii/ Monster Hunter

Tomb Raider (2013)
BioShock Infinite
Skyrim

Might add more later ...

There have been several, but the one that stands out the most was Xenoblade Chronicles! I've dumped a year into that game (off and on of course after a straight run to beating it), and still haven't got everything.  JRPGs being my favorite genre, it's pretty much the only game that got everything right about what I love about them.

Alone in the dark (the improved ps3 version)
ghostbusters the video game.
Enslaved
Darksiders.

Siren New Translation for the PS3, my favorite last gen horror game.

And I forgot to add wolfenstein the new order. It just came earlier this year, but the game went under the radar by many gamers due for being released a week before Watch_Dogs