I've played this only a little bit, but I'm already loving it. I got this a couple of days ago(on 10/10/2014), and didn't play until today. In those two days I noticed it was updated regularly, and they did not take long at all to post a bugfix, showing they listen and respond to the community. I know some devs take days to fix a bug no matter how small it was.
The actual gameplay reminds me of a slower paced and more strategic Paranautical Activity. Enemies are quite varied in their attacks: Some are stationary and repeatedly shoot slow moving energy balls that must either be dodged or jumped over, another with a similar attack pattern, but releases lasers in multiple directions that must be jumped over. Some enemies will go for the ever classic "chase this ♥♥♥♥♥♥ down and smack him" approach to attacking you. Some won't even directly attack you, but will walk around the room, away from you, and occasionally let out a floating mine that will home in on you if you get too close and explode. There's even one that kinda stays stationary in the air, shoots you once, then goes invisible and teleports/moves to another location quickly and reappear and shoot again. The enemies in Fancy Skulls are interesting a fun to fight.
Personally, I like the direction they took with the art, but I can understand that it's not for everyone. I also didn't really notice the music, but I'm not really the type to notice the music unless it's either in your face or completely absent.
There are 7 different weapons in the game, and unlike paranautical activity, you can get 'Weapon Mods' for each of the weapons, giving them different boosts. I won't go into all of them, since there's a lot
of Mods, but for the Revolver, which is the default starting weapon: There's a mod that has a chance to set enemies on fire, there's a mod where every time you jump you automatically place a single bullet into the gun, which makes getting more shots in without reloading easier, and a mod where the first shot after a reload does double damage. Each weapon has at least 6 mods for it.
This game is still Early Access, so the game will only get better with time, and considering how good it is now, I'm really looking forward to release. If you haven't picked up on it yet, I definitely recommend this game.