X Zero, at least in my opinion, definitely captures the simple enjoyment of old games. Just running, gunning, and doing the thing. I like that. The music isn't half bad, either. It's a bit repetitive after a while, but still has a nice sound it that makes me wiggle my gun to the beat. (Though not in public.) I'd wondered at one point why the gun was silent, but then I realized...I fire it constantly. So it's a fun AND smartly designed game.
Good job, dev.
Praise aside, I did notice on occasion that the game would speed up, sending me flying forward or quickly jumping around, often to my detriment. Not sure if this is on my end or the game.