I love that you leveraged the verticality of the isometric 2d jump to also give the player the gravity attack. I want to echo what the other players have said, that this is a fantastic proof of concept. The presentation is really nice too, having the fading environmental elements gives a lot of depth. The weakest point of the presentation is probably the font, just because it doesn't fall in line with everything else (white on light grey/white at the beginning means the player's attention isn't called to that text.)
Basically, there's a moment where the player (me!) goes "THIS IS WHAT THE GUN DOES!? WOW" and I think there's a version of this game where that feeling gets fully exploited to make this an amazing experience.
I think the customer spawned in a wall every time I refreshed, though. :(