DRG is a 4-player co-op dwarven-mining-roguelike... I think. The basic gameplay loop is that you drop into a randomly generated cave with up to 3 other friends and have an objective: mine a certain amount of X, defend a driller, find eggs etc. There's a few ways of doing co-op games; either it's a long campaign where you have to organise playing with the same group of people and make progress together, or games like this where you can drop in with random people, play for 20 minutes then do something else. Both have pros and cons, but I do find with this game that I lost interest pretty quickly just because it's mission based. However, it's highly polished, hectic, and a lot of fun together.