One of the most "indie" titles of all time. An absolute classic to play. Although the original does have it's fair share of bugs, playing through it was a blast!
Basically, you take the Metroid-vania style of games like Hollow Knight and Dead Cells, and you give the player a bunch of unique and fun guns, and give it an EXP system that punishes failure with weaker guns, but rewards you with upgraded weaponry as long as you play right. Top all that with an interesting story that's simple, but gets you invested, a ton of unique options for weapons that'll have you replaying the game to try them all out, and ALL FOR FREE!?!?
Please play this game. You won't be wasting your time. And even if you don't go through the effort to do the "True" ending, and you only get the Good/Bad endings, it'll be a service to the world if you JUST... PLAY IT!!!