Very nice little level. I particularly like the final boss's room's layout, and the "introduction" section.
It might be fun if the spinning panels on the miniboss bounced Super Pellets around randomly, rather than absorbing them. To set this up, change their Extra1 to -1.
I also had some bad lag problems in the final boss room. At a guess you have too many trigger sprites- I know that having a dozen or so force fields on-screen at a time does bad things to framerate, and having the level spinning regularly might make things worse.
There are several places where the background sprites are improperly aligned that you should fix. Sorry, I wasn't keeping a list.