Depends whether you prefer singleplayer or multiplayer.
Blood and bacon ($0.99, pretty much pig left for dead, Singleplayer)
Garry's Mod ($15, Probably the best game on steam, Multiplayer)
Undertale ($10, Great story based game, Singleplayer)
Half Life 2 ($10, Story based game, Singleplayer)
CS:GO ($15, I don't play it but a lot of people do, Multiplayer)
The Forest ($15, Survival horror game, Multiplayer)
Rocket League ($20, Pretty fun game about car soccer, Multiplayer)
Stranded Deep ($15, Survival game that takes place in the sea, Singleplayer)
Gang Beasts ($15, Funny game with great ragdoll physics, Multiplayer)
Replica ($3, Great story game with many endings, Singleplayer)
The Stanley Parable ($15, Probably my favorite story game, Singleplayer)
Surgeon Simulator ($10, Not as bad controls as people say, Singleplayer)
Goat Simulator ($10, Awesome game, Singleplayer)
Octodad ($15, Extremely creative game, Singleplayer.
Might want to wait until the summer sale, games prices drop enough for you to get around 3-6 games depending on the game.
