Great game, terrible player community.
The game is free, you can spend real money to buy characters and runes to power up your characters or you can earn in game money by participating in matches.
The problem with this game is the hostile user community which is why I didn't give it a better score. Matches take place online where you are randomly matched with other users on a 5v5 or 3v3 map. The players you are forced to team up with are typically whiny teenagers waiting to "nerd rage" on you for any mistep in your gameplay. The players make this game nearly unplayable.
Recently there has been a number of updates such as the ability to report player behavior that should help clean up the community. The online matches vs bots have also been introduced which provides a less competitive experience.
Overall, I would recommend giving the game a shot since its free, just remember my warning on the community so there are no surprises when the insults start to fly.