I've played a lot of the maintream stuff (COD, Battlefield etc.) but my favourites of all time are:
1. Metroid Prime Trilodgy (Awesome games, great music, storyline & gameplay)
2. Minecraft (build blocks, explore blocks, kill blocks & blow blocks up. What more do you want?)
3. Halo Reach (So many great memories on this game with my friends, made many fun maps on Forge too)
4. FTL (Not great graphics, but everything else is superb. YOU COMMAND A SPACESHIP I MEAN CMON)
5. Undertale (Again the graphics are crap, but graphics mean nothing to me anymore : P awesome story in this)
6. Skyrim (what a gaaaaaame :D, hated that i had to kill the dragons instead of taming them though .-.)
Opinions?