This entry is extremely impressive! I played with a gamepad and it felt good to play. It was one of the few entries that I wanted to keep playing. I can't really say more than what everyone else has already said; it's really good.
I will however state my two gripes:
1) The hitbox on those flying ghosts is way too big. I can't tell you how many times I got hit despite killing them.
2) Having enemies respawn when you reenter an area is fine from a gameplay standpoint, but the fact that they stay spawned in when you exit an area means they can ambush you from offscreen if you're near the edge of an area. Also it gives rise to a bug in which quickly going back and forth between areas causes a LOT of enemies to spawn in and stack on top of each other.