I know you have one.  That one game that you always go to time and time again when you need a fix.  That one game you can always come back to even years after it's been released and have a good time.  What is it?  For me:

• Street Fighter 4 :  No matter what hot new game is on the market, I'm always up for a little fighting in the streets.  The community is loyal and talented.  The fights are always intense and there's always more to learn.  Street Fighter 4 may be the perfect video game.
• Final Fantasy Tactics: :  The inspiration of this thread.  I was bored last night at work and fired up the Vita.  I don't know why I bothered since the Vita has no games.  I saw FFT and fired it up.  Now it's like 1998 all over again!  It edges out Advance Wars DS because the characters are more personalized (all named after ex girlfriends) Gotta play it until I finish it....
• Call of Duty (Series):  Say what you will about the series but it sells well every year for a reason.  The games are fun!  Grab any one of them, log into Team Death Match, and enjoy!

Mario Kart (series - my favourite is the latest)
Animal Crossing New Leaf
Street Fighter (series - but my favourite is SF III Third Strike)

Any Tekken bar Tag 2, mainly 6... I basically spent most my time dressing up characters in 6.
Super Stardust HD
CoD, it's quick and easy (Black Ops 2 but that's a mess now, so prob going back to BO1) with my brother mainly, don't play it otherwise but he plays it a lot.

For more adventure long winded adventure, FF12.

Befor Smash 3DS came out, I'd go back and play Brawl every once in awhile. The only other games I do that with now are Guitar Hero or Rock Band, namely Green Day: Rock Band. Otherwise, I'm always up for replaying one of the Zelda games, but I try not to do that too often so I still have time to get through my backlog/play new games.

CoD is def up there for me. But there used to be a time it was a Total War game. If I was even a little bit bored I would turn on the PC and play.

Uncharted 1 I replay regularly too

Little King's Story-I dunno why this game just always makes me feel good and I love playing it.

Ace Attorney- I can replay each Ace Attorney game over and over again and still have fun for some reason. However the longer its been between play times the more I enjoy the return.

Animal Crossing- No matter what this game is still the best to come back to, even if I get bored 2 months later.

Tekken 3

This is hands down the best fighting game ever created.

Soon it will be Gundam Ex Full Boost

Dreamcast games cuz they're arcade

Basically many arcade games lol

Also currently trying out Assetto Corsa

Smash and Mario kart easily

Tetris, Mario Kart. pinball, games by LucasArts
Non-VG: Bela (Belote), chess

Battlefield FTW! Oh, and I find Time Crisis really fun!