I don't expect the scope of the game is going to grow much but a couple of suggestions:
Speedrun mode- playing against a timer with your personal best tracked.
Score mode- earn points for kills and explosions, lose points for time used, personal best or high score list tracked.
Something to add some more replay incentive for whats already there.
Energy recharge feels rather slow, especially if you make a mistake and fall and have to wait between floors to climb again.
I also beat the three difficulties in a single run, so it's perhaps a little too easy.