DOTA 2 is a free to play game, that offers great competitive gameplay and great visuals.
Gameplay vise DOTA 2 is a direct decedent of DOTA the first game of this genre, it is extremely fast paced and has huge variety from the get go. You have all 100+ heroes available to you so I suggest playing a couple of games vs bots if you are new to the genre, since the game is challenging and competitive and people tend to be very invested in the outcome of matches so if you cause your team to loose they will point that out in very mean ways most of the time.
Another great part of the game is that you have zero pay to win elements, money can't buy anything with an effect on gameplay which is a great more over there is nothing affecting you outside of the round, there are no permanent upgrades or any advantages to long time players like bigger hero rosters or buffs, the only thing you can buy are visual items for your heroes, or different hud's that are designed by people in the community plus you can get them free since they are regularly given for playing the game.
As I said the game is challenging so I do not suggest it to people who have very little time to play games, since one round can last from 20-60 mins and you will still be learning new things about the game even after 100 games, so it is definitely time consuming.
The good thing is if you have the time to invest no other game comes close to winning a close DOTA 2 match, and once you have felt that feeling you will be hooked much like the hundreds of thousands who play it.
This is one of those games you just have to try yourself and since it is free you have no reason not too.