Risk of Rain

Here is the official website.

Risk of Rain is a game set in the distant future.  In this reality, space travel is an everyday thing, and people and cargo can get transported through space on "space trains."  One special space train is carrying important cargo.  For an unknown reason, it crashed and lands on a mysterious planet.  There is only one survivor.  You.  The game plays with perma-death as its main feature.  This means that once you die, you die.  All progress you had achieved up to the point of death is lost, and you have to start again (unless of course you rage quit).  

There are ten classes (as shown above).  They are from left to right, top to bottom:  Commando, Enforcer, Bandit, Huntress, HAN-D, Engineer, Miner, Sniper, Acrid, and Mercenary.  There is around 20 different enemy types, and 10 bosses.  The levels are randomly generated, so it is a unique experience every time you play.  There are plenty of items in the game (over 100) that power you up and help you explore the planet and find the teleporter to home.

The game also has a co-op multiplayer feature, so you can kick alien butt with a friend, and the difficulty for this game is quite high, so I wish you good luck if you choose to play it.  You will more than likely rage quit.  I have many times.