From a look at the recent press preview event, I'd say it's World of Warcraft battlegrounds with League of Legends champions and some World of Tanks elements. Sort of. There might be more.
As the above implies, we recently had the opportunity to take a look at some preview footage explaining how the game worked and what the actual play would be like. The game is certainly looking nice, especially when you consider that it's a free-to-play browser game built in Unity. But the proof is always going to be in the gameplay, and while it's hard to say for certain how well it delivers from mere preview videos, it's certainly intriguing.