TF2 is a free game that is a battle between two teams (blue and red) for something. You are allowed to choose one of several game classes, each of which differs both in appearance and characteristics, and in the weapons that he carries with him and uses to destroy opponents.
In principle, the game is very diverse. There are a bunch of game modes, and a bunch of guns with clothes that can be knocked out or crafted from other game items.
The gameplay is also varied thanks to the same game modes (all sorts of pushing carts, capturing points, flags) and game classes. You can always try yourself in a different role and in a different mode.
I also note that the game is free. Yes, without spending money, you will be limited in some game functionality (transferring items, number of slots in inventory). But without investing money, you can play exactly the same as other players, because there is no donation that affects the balance - only decorative hats, clothes and skins.