Warframe! What is it?
(TL;DR at the bottom)
It's a free-to-play third-person shooter set in some sort of futuristic sci-fi universe. The story-line doesn't really matter, as the games main focus is co-operative focused missions! They have some lore and some actual characters, but you'll find yourself not caring that much about them.
The coolest part about this game so far as that you level up everything individually. Your warframe, (AKA space suit), primary, secondary, and melee weapons all progress independently from each other depending on how often you use them. More importantly, you can install mods on everything to further specialize your suit and weapons. (As an added bonus, you can also change the colours to further differentiate yourself from others).
They've got three different enemy factions to play against, and you fight on multiple worlds with three or four different types of missions also thrown into the mix. Obviously, they all require different strategies to fight against.
The best part about this game, is that the only advantage players have over others who pay versus earning it, is that they get stuff a little faster. Too my knowledge, there are no exclusive weapons or armors to paying players vs free players. (I'm sure they get some kind of bonuses, but I am fairly certain it's not gear). It's also great that players playing for free can earn anything in the game. (Albeit at much more effort).
That's about the game in a nutshell. For anyone currently playing, add Fappley, (that's me), and we can take on some missions together. As for the rest of you, sign up already!
TL;DR: Lots of pew pew and explosions with friends. Also, it's 100% free.