Counter-Strike 1.6 is a fun play, it is what you would expect from a Counter Strike game, despite running on GoldSource and still having a large player base of over 9000 active players.

Garry's mod is an excellent sandbox experience with a huge selection of user created content inside of the workshop. Mess around with HL2 NPCs or play murder mystery with a group of friends.

Ricochet is probably by far one of the least played Valve game with only having 2 players on at the time of writing this review. It has very basic gameplay and has bugs with mouse movement.