It's free to play and fun to boot -- if you're a fan of DotA then it's worth a go!
A big complaint regarding other DotA-style games is that the heroes are identical; only with a slightly different look and name. Not so here. You may recognize a few similar abilities here and there, but that's about as far as it goes. The champions in LoL are entirely unique.
While the game is free to play -- additional champions and various extras must be purchased. However, you can also purchase new champions through points which you gain by playing. It's a nice system -- if you don't want to spend money, you don't have too, but you are continually rewarding for playing the game, and especially for winning!
I have played DotA since way back, and will likely move to LoL exclusively. It isn't DotA, but it is new and fresh, and just as fun. At very least, if you enjoyed DotA - it is well worth the time to try out and give it a chance.
https://signup.leagueoflegends.com/?ref=4c4f68ca45df7