Action games need special treatment when it comes to abilities, just take a quick look at Terraria or any other for examples
Using number keys for action bar is ok, except you would expect to select that ability-tile not specifically use it.. also mousewheel to scroll between spells
Common spells could have their own keys ie. Q, E, R, F (such as speed boost spell)
I also would consider platform-ish like mario world tiles, since it looks more ok from sideway look
right now the transition from over to underworld doesnt look too good
take for example sand-land.. the sand should have a top, and a bottom, that way it looks like you are standing on ground
right now it looks very plain, i guess
these are only ideas though! I'm very hopeful that you consider the actionbar changes, since right now its very slow for me
i want to be able to scroll to a spell and use it immediately
the part about common spells having permanent hotkeys is just an idea, i liked the hook in terraria having its own key since that gives mobility without having to change spell
great game so far.. =)