An early progenitor of the modern roguelike genre, Risk of Rain is a great 2D action-platformer to play, that will beat you into the ground with no remorse. This game is hard, very hard. The core concept is that the game gets harder the longer you play, so as a player you need to tradeoff quicker progression towards the final boss with more time to explore and obtain upgrades to scale you up in damage and defense. It's a pretty straightforward formula, but it offers tons of variance between runs. Different characters, each with their own abilities, playstyles, and builds, keep things fresh over time, and they are all designed in such a way as to be uniquely engaging to play with, without overlapping in playstyle.

This game has recently had a remaster in Risk of Rain Returns, which by all indications is a superior version of the base game, with changes made based on the lessons learned from the sequel. Nevertheless, Risk of Rain, the original, remains just as playable now as it did 10 years ago, and will still test your abilities. Not to mention, it has an absolutely banging soundtrack. Truly a game that you can vibe out to while simultaneously sweating your ass off playing.