Just checked out some of the others:
-Dr. Moonlight's Happyworld: Other than Xoo, it's one of the standouts. Something about the graphics for the creatures, the setting, and the puzzley nature of the game and some of its combat all make for a nice blend. There's something neat here that more people should check out.
-Ultra Frontier QQYYZZ: Not too shabby for what it is, though I wasn't able to get very far.
-Star Dartle 2000: Shmup with an interesting wrinkle. I have NO idea how I'd keep up with the count on my own, but it's a very neat idea that adds a touch of complexity that I've not seen elsewhere. :)
-Owlbears: Simple, but the enemy types' varied behaviours add just enough complexity to it to bump it up out of the monotony that would be there if there was only the charging monsters.
And again, Xoo is a delight.