I think the fact that the game is presented in an isometric manner, but uses cardinal controls makes it so that the player feels a "disconnect" between the two. Maybe I'm a bad gamer, but I felt like I had to constantly think about which way I was going to go when pressing a button, rather than just doing it from intuition. This, coupled with the fact that the characters can fall off the platforms leads to a little bit of an unpleasant experience in my opinion. The atmosphere of the game worked for it, for sure, and the characters were likable. The joining mechanic was interesting, and I would like to see that explored a little more.
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I think it already helps, if the camera is not in perfect 45° but 40° angle, so the player can figure it out, if he needs to, but you keep that isometric feel. Also you could have the floortiles become brighter, the higher up they are to make depth perception easier. One last notch i recommend is syncing the particle effects with the beat of the music. All in all the game has a good foundation of ideas and i enjoyed it a lot, well done :)