I'm the music man for the game, so I'm pretty biased all things considered but I'll try to be honest.
A game with far more emphasis on the Castlevania than the Metroid, the game adds a craftable weapon system into a game with much more focus on the precision platforming and fighting that the old NES Castlevania's did so well. It will kick your teeth in on some of the levels, even at the lowest difficulty, so definitely learn to use the weapons well.
It is still rough around the edges, but constant updates and improvements are still happening with new levels. If you can't get enough old school demon-whipping you will find a great time here.