Football Manager 2014, but since its been removed from store, I can't add it... So I added XCOM: Enemy Unknown

No Mans Sky. tested and approved after 10 mins of gameplay no

Nightmares from the Deep: The Cursed Heart

M&B

Binding of Isaac: Rebirth

Terraria

I picked FF7, even though I don't own the Steam version. I've lost count of the amount of times I've replayed that game over the years despite the bizarre mish-mash of character model design throughout the game & the somewhat all over the place story-line or lack there of. I don't know why I liked it so much, but I did & still do. If not for that I would have probably picked Rocket League or Battle Block Theatre as both are addictive fun & will probably get enjoyed (with extra helpings of frustration chucked in) for years to come.

Final Fantasy IX

Star Wars: Knights of the Old Republic II

Thief II

At first I went for Total Annihilation, but then I changed to Railroad Tycoon 2. I wish I could vote for both :(

Dota 2

The Longest Journey

Quake Live

FOREVER

Fallout 3: GOTY. I have literally played several hundred hours of this game, and I still love it just as much as the first time I exited the Vault. I don't have the Steam version, so it doesn't show me having any playing time, but I have found there are so many good mods out there that make the experience last even longer. Bittercup as a Companion FTW!;)

Long live the queen !

Cave Story+

Final Fantasy VII

one of the games i always come back for (since PS1) and play it for at least a few hours... :D

Silent Hunter III

Portal 2

Grim Fandango

Deus Ex or VTM Bloodlines were definitely runners up, but without modification, I think Grim Fandango's extreme stylization helps it... stand the test of time... a bit better than either of those two. (When I replayed it as the Remastered version the first time, I used the old controls and old graphics and it was just as awesome then as it was on release.)

Rome Total War. It's more then a decade old but still incredibly fun and it actually still looks decent.

GTA San Andreas

Command and Conquer Tiberian Dawn isn't on steam, so I don't know what to vote for, GTA III or something, I realy dont know.