I don't know if the elevator is hiding the level loading, but if it's not I think the game would work better rhythmically if they were less frequent. At the moment a lot of the game is spent in the elevator waiting for the next level.
Also, on OSX the right-click to fire while holding something doesn't really work, as a right-click is a two-finger click. If there were keybinds for firing, this wouldn't be an issue.