I think it's a good start. You should remove the timer and tease content that isn't in the demo, or you should give more warning so it's not abruptly over. Or you could make it into a soft-cap ending: After the timer is over the XP is reduced to 20%. Add some ascension system with unlockable perks and this could go quite a lot.
Maybe skip the 3D graphics or make them more drawn, so they don't clash as much with the 2D graphics. Sounds is fine.
Overall it's a small, nice game with much room for growth.