I miss party games in the vote, because I love games like Wario Ware, Dance Dance Revolution, Rock Band, You don't know Jack and Buzz. But I never liked other multiplayer games like shooters, MMOs or racing games.
Most of the time I play alone. RPGs und RTS are my favorite genres. And interesting indie games in general. Oh... and I am addicted to Towr Defense games, I play every single one of them
Diablo 2 (LoD) is my favorite game of all time!
Other favorites are the Anno series, Worms and Terraria. Terraria is a must have title! You can get it at Steam for about 5 bucks when it's on sale. I played about 200 hours already and it never gets boring because there is so much to discover. It's an exploring/action/building/crafting game with small RPG elements and many connections to Minecraft. But there are more monsters and way more different items. Give it a try, especially if you like this old fashioned retro look: http://store.steampowered.com/app/105600/
My favorite platform is the PC, but I also enjoy 3DS/DS, PS3 and Wii games. And from time to time I have to play some old DOS or SNES games as well. Like Lemmings 2... it's still amazing today.