Wonderful game. The mechanics are simple considering it's just shooting a single weapon and sometimes spells, but with the amount of enemy variety that actually DOES different things and aren't just increasingly spongey (I like that nothing is really spongey in this game), it does well enough that it doesn't get boring for the span of the game. I WAS going to say the game feels really easy, but World 3 onwards changed my mind. That mage fight, man, it's intense. Considering it's not meant to be "hardcore" or anything, the difficulty's at a good place honestly.
The graphics are one of the merits of the game to me, it's simple, cute, but it's totally polished and the animations are smooth. The music's not bad, and the sfx IS pretty satisfying, not that I know too much about sound. I would say the troll should get a different bullet graphic to indicate it does double damage, but that's about it.
All in all I can't think of much I could gripe about, except for maybe one thing. The way potions are done in regular battles make the levels a curbstomp long as the player doesn't get insta-killed by those goddamn bomb wisps or swamped by enemies, which is practically impossible if you've been upgrading your damage properly. Since potions seem to have a high drop chance after I reach 2/4 hearts, and I get a LONG ass invuln time (that should be cut in half), there's next to NO chance I can't heal back to safety immediately no matter how many times I screw up. I never even bothered to level my hp until the final boss, one level in regen and one in potion efficiency was already more than enough! I'd say outside of crate drops, the potion should be a once-per-level "spell".
I'd say that's about all I can think of to say. Perhaps more varied map hazards than pools of stuff that affect/deny movement would be nice. I like how you used the overused 3-star system in a way that actually involved different objectives for each level. The third star for the final boss was clever, heheh. Can't find the secret birds though. Anyway, it is a great game that I had the pleasure of playing, definitely one of the better games on Newgrounds. Good luck with the Greenlight, mate!