Games That Were So Good That You Played Them Again and Again.

Portal 2! I've beaten it 7 times now I believe, love it just as much each play through. Puts me in the happiest mood.
Non-steam games: Pikmin and Donkey Kong Country. I've spent years replaying both of them, still my fave.

The one and only Morrowind.

dead space 1 and 2
assassins creed ezio trilogy
rollercoaster tycoon 1 and 2
stronghold crusader

GTA San Andreas , this game was so good I played this so many times that I can't remember. And this was before Steam.

Let me think about this:

• Armored Core
• Metal Gear Solid 1
• The Legend of Zelda
• Command and Conquer 95
• Red Alert 95
• Pokemon Red
• Final Fantasy VIII (8)
• Tales of Vesperia
• Halo
• Killzone
• Half Life
• Diablo
• Warcraft
• Earthbound
• Mario Party
• Paper Mario
• Super Mario RPG
• Custom Robo
• Animal Crossing
• Gunship
• Desert Strike
• Star Wars Knights of the Old Republic II
• Grand Theft Auto Vice City
• Phantasy Star Online (across multiple Consoles: Dreamcast, PC, Xbox, Gamecube)

GTA 3, Vice City and San Andreas :)

The Saboteur
Mafia II
Sid Mayer's Railroads
Counter Strike (any)
Fallout 3
first Call of Duty series

Half Life 1-2,Doom 1-2-3,Quake 1-2,Heretic 1-2,Hexen 1-2,Diablo!!!!!!(1-2-3),expansions ofc
Gaming since 1988 and still going:PPPPP

bomberman

I feel shit for it but I don't really return to fixed story, regular games. I played a lot of Fallout 3, NV and some TES games but mostly because haven't finished it and played it in a different manner, so it's still kind of new content. I remember too much about the games, making it less challenging and usually more easy to min-max it without much effort.
I had I think 5+ playthroughs of Dishonored for various achivements and I still love the game, but it became too easy and predictible after all that time. Sometimes I really wish I could make myself forget about these things, but a lot of game-releated things are just like chalked up in my mind, can get a little blurry, but a situational trigger refreshes it. (Like breezing through etherlords 2 after not playing it for a decade still remembering what combinations and decks I found useful and effective)

Prince of Persia SoT&WW, Rome TW.

Dragon Age
Call of Duty (first and second games)
Skyrim
TWD

Mirror's Edge
But also because it's so short, you can play it again and again

Star Wars: Knights of the Old Republic. I've probably played it 9-10 times (the old non-steam version), I just love it!

WC3 ROC + TFT

The Witcher 2,3
Mafia II
Black Mirror 1,2,3
Mass Effect 1,2,3

Pandemic 2.

Hmm...

• Mass Effect 1 & 3
• Dead Island
• Dreamfall: The Longest Journey
• Resident Evil 5
• Super Mario Brothers
• Portal/Portal 2
• Half Life 2
• Fallout 1 & 2
• Carmageddon
• XCOM: Enemy Unknown
• Star Wars: Knights of the Old Republic I & II (mostly first one though)
• Star Wars: Yoda Stories (primitive but funny)
• Star Wars Rebellion
• StarCraft & Brood Wars
• Krush, Kill & Destroy 1 & 2
• Total Annihilation
• Borderlands 2
• Risk of Rain
• Battlezone 2: Combat Commander
• Robocop 2 or 3... (NES)
• Duck Hunt (NES)
• Batman Returns (NES)

Multiplayer games:

• SpringRTS (XTA mod)
• UrbanTerror
• Counter Strike (classic)
• Soldat

Order of games is random, this is more or less what I remember.

[Edit]
I forgot about Soldat xD

How can you people play a game twice :o?

I dont even play the re-master versions of some games that I have played when I was a kid, for example -> Day of the Tentacle
I maybe play again games that I haven't finished and have lost the saved game and thats it. (not all games support steam cloud)
There are so many new games out there to play so playing the same game again and again I consider it a waste of time... :o

The same goes with movies , I watch a movie ONLY one time ... :P

Im playing runescape oldschool and Diablo1 at the moment. Also finished plying Soulbringer recently.
Edit: Also, played Far cry 1 a few too many times.

Civilization, Colonization, TES:Daggerfall, Seven Kingdoms 2: The Frythan Wars, Tyrian, Master of Orion 2, pINBALL fx, and few more...

Edit. Yes Diablo 1 too

jagged alliance 2

Majesty