Free is obviously a big limitation. Honestly, I feel like the only free game I can actually recommend at this point is Dota 2, although notably you really need someone to tutor you to get into the game. Its just too complex, too team-focused, and too deep to get into without a more experienced player to guide you. That said, if you do get through the hundreds of hours of learning, there really is nothing else that compares.

Outside of this, now that Steam is pushing developers to make demos again, try giving some of them a shot. Its a fun way to get a sampling platter of hundreds of different games, especially during Steam’s festivals. If you enjoy it enough, you can always buy the full game later.