Glitchskier is really fun. It's sorta like a shmup version of Downwell. The levels are procedurally generated, dying starts you back at the beginning, there are loads of power ups, and you can actually change the color palette of the game through unlocks. Beating the first two bosses was fairly simple but after that it gets really hectic with many enemies that continually track you until they're destroyed. Haven't tried endless mode yet but I might get to that after I've beaten the campaign first.
I can vouch for this too. Great game and, in addition to what you've said, I'd add that the music is fantastic. Also like the use of ASCII characters and other computer-ish objects. Well done all around.