Here's how to make a list:

• Need for Speed 4: High Stakes - classic arcade racer. I use it as an Initial D simulator by adding cars from there. Then it ironically becomes the best Initial D game out there. The vanilla game is pretty fun too.
• Spider-Man: The Movie (2002) - this was the first ever video game I remember playing. Basically sums up my early childhood.
• MUGEN - the ultimate crossover game. Epic as fuck. The only fighting game I'll ever really play (I still love Tekken though)
• Grand Theft Auto V - best GTA, so far. What else can I say, it's GTA V and sandbox is my favourite genre. It's just, like, the best real world simulator. And an even better cop simulator with LSPDFR. (Note: this is for single player, I've touched Online about... twice I think)
• Garry's Mod - for me, this is the game of all games. I particularly love it for the roleplay platform it provides and the sheer amount of quality add-ons. It's just a shame the community is defined by memes and kids.
• The Sims 2 - Did I say Spider-Man summed up my early childhood? Well, ok, this game did it almost tenfold. This is the best Sims game - period. I've played this... practically forever.
• Insurgency - hands down the best FPS I ever played. People actually die when they get shot at. And it's my favourite setting of Middle Eastern desert insurgency too. And it runs on Source. Can't get any better.
• Half-Life - I so wish I had played this even earlier than when I did in 2012. Shooting aliens, atmosphere, the father of everything after it - you know.
• Star Wars Battlefront II (2005) - Best star wars game ever. Tied with Empire at War, but edged out by just the sheer amount of fun.