Good spend of half an hour. The music is a bit repetitive but the graphics are spot on. I hope the suite of upgrades you're planning for the full game are diverse like the bombs, arrows, and spike ball, not mainly number go up types. It was fun managing risk of going in to bounce a spike ball or set off a bomb or keep multiple targets nearby for the arrows.
I agree with the other folks saying there's a progression stall on level two where you're not strong enough to amass coins for combat upgrades and gems are coming in slow. Maybe a coin-gem exchange would help smooth that out.
Again, you've got a good foundation here. Will be keeping an eye on it.