Darksiders , it might not be the best game ever but i loved every minute of it.

i see that there is no Love for Crash Bandicoot in this thread yet

Gubble.

My current top 5 favorite games also fall in that category you described.

1) Minecraft - I really don't have to explain why, right? xD
2) Scrapland - Before MC came out this was a game I would play every year. It's such a shame it's so underrated. I played it 15+ times.
3) Postal 2 - Yeah, say whatever you want but that's the best way to blow off some steam. It also helped me to discover that I wanted to become a game developer.
4) Amnesia: TDD - The best horror game I played, the first horror game that actually managed to scare me and I played many of them and I don't get scared easily.
5) Quake 3 - Old school action FTW. I only play against bots, and believe it or not, I have tons of fun.

The Incredible Machine and Commander Keen 4, the first two games I ever played.
Chrono Trigger. I remember me and my big brother playing it for hours, with his strategy always being better than mine.
Then Starcraft and Half-Life. Nothing better than the sound of a few Marines dying painfully. Applies for both games.

Cyberstorm and Cyberstorm 2: Corporate Wars on PC. Star Ocean: The Second Story on PS1.

I suppose for me it's the original Portal and probably Mario Kart Double Dash...

Timesplitters 2 and 3

Conker live and reloaded

Jet Set Radio

Original Ratchet and Clank

Digimon World 1. I'm quite sure they could boost PS Vita sales if they release another game like Digimon World 1.

Action Quake 2, Killing Floor and a bunch of other games

Half Life(series),
Mass Effect(series),
Metal Gear Solid 1,
Elder Scrolls(series),
Splinter Cell(1-4),
Commandos(series),
Team Fortress 2,
Portal(series).

Final Fantasy VII, Dungeon Siege 1 and 2, Mass effect 1 and 2 (have to play 3 yet), Bastion, Borderlands series, Bioshock series, Darksiders series, God of War series, Prince of Persia series, Portal series, The Witcher series, The walking dead and ofc To the moon.

From older consoles: Streets of Rage series, Sonic 1,2,3 & Knuckles, Space Harrier, Cadillac & Dinosaurs, The punisher and a few more which title i can't remember now :)

Edit: Oh shit, i forgot Metal Gear Solid 1!

The old Tomb Raider games.

Just cause 2.

:)

Metal Gear Solid! :)

SNES Chrono Trigger. Finished it ~20 times, and every time it felt like I was playing for the first time. Now and then I play it again, and the music always keeps me thrilled

Borderlands

Grim Fandango
Fallout 2

The Jak series. I always played 1 through 3 whenever I was a kid. The jokes that Daxter always said made me smile and the opportunity to just go Dark Jak made me go wild. I never got to play the last two Jak games and the Daxter game, but they will be in my hearts as well even if people say they suck because they are part of the Jak series and I will see them as the same fun and exciting games as their predecessor's.

I'll have to go with Monster Rancher 4 for the PS2 (and PC SX2). The Monster Rancher series just had so much potential...

Shining Force 2. Most of my childhood consisted of coming home from school and playing it for hours.

Arcanum.

Portal 2; the ending was so epic I cried. Also Mass Effect 2 and Legacy of Kain Soul Reaver.