Risk of Rain is a very simple 2D platformer game. I have played it in single player as well as in multiplayer. What you basically do is go through levels killing enemies and bosses while leveling up (you reach max level kinda fast) and collecting items (They stack and there are a ton of different items that you can get). In addition to different classes you can choose from and different items you can get, there are artifacts that you can unlock that completely change the gameplay. For example there is an artifact that forces only elite enemies to spawn, or another one that makes the level spawn only one type of enemy. All around it is very enjoyable to play but it can be somewhat tricky to get all the achievements. If you are looking for a game that can be complete in 10 minutes (a run can be completed in 10 minutes if you know what you are doing) but at the same time can last hours upon hours, this the game for you.