One of the best Coop games around with a classic gameplay genre: roguelike hack 'n slashy, with four different maps to play on: two adventures, a survival campaign and a hero defense mode.
We can also consider this game a kind of RPG, expecially in the new Sun Temple campaign, where you can choose between six total classes, each with their own abilities, skills and upgrades that you can get with the money and coins you can find in your journey, while you fight your way to clear the dungeons you're in from it's monsters and look for the secret stuff that are waiting for you, all of this together with a golden soundtrack.
It may look that simple like this, but there is way more stuff in this game that i'm not going to spoil to you; you'd better find out by yourselves with your friends and family.
The best discoveries by the greenlight system is stuff like this, just to go a little offtopic. Peace.