Robocraft: It's like a mix of Minecraft and Robotwars. It's so fucking fun, and 100% NOT P2W. The devs even made a statement saying they would never go that way and stickied it on the Steam forums. Brilliant and addictive game. The round layouts are like WoT, but they don't last 20 minutes, and if you die you can leave and queue up without having to wait a million years. Also no repair costs.
Seriously, if you play WoT, or Warthunder, or anything of the sort; give this game a go. It beats all of them combined. Also there are hovercrafts and flying robots too. It's only in alpha and I've rarely noticed a bug.
Mechwarrior Online was nice last I played it. It's fans got really pissed off with the devs for asking $500 for a gold skinned robot though. That was quite a while ago though. IDK how it's going now.
Hawken: Shit, lag, shit. More brain-dead than Call of Duty. Don't bother.
Edit: Here's the robocraft link [link]http://robocraftgame.com/download/[/link]. It can be on either Steam or Standalone. The download is pretty small. Play it. Play it now.