I must say I'm highly impressed by what was achieved here. Having grown up to Sega systems, Alex Kidd filled a large part of my childhood (and also taught me the bittersweet frustration of getting far into a game just to run out of continues ha-ha). Anyway, please keep up the good work, thank you for bringing back so many memories.
As others have mentioned, I'd be particularly happy to see a Zillion HDification, if you ever work on that.