Fun game, looks really good with the lightning in 2D. Upgrade system is also nice, but feels a bit unbalanced near the end. I maxed out the gun, but the purple enemies were still just huge damage sponges. They were also able to damage me while not even touching me yet. It takes a lot of time to get all the way back to the surface to upgrade, which is not necesarily a problem, but it would be nice if you also restore some health or something or buy health packs for less money then a upgrade (like 50 bucks). I think then the game would be a bit more balanced and fun all the way until the bottem!