Well, I now just played a little bit of your mod and wow... it could use some work.
Some of the bats in the first area aren't like some of the...other bats. They only just fly a tiny space up, then back down, unlike the other bats who'll fly like those in Cave Story.
Holy Crap! Those blue squishy things coming down from the ceiling after getting my gun scared the hell out of me! D;
People who do not really take notice that the door can attack you will just waltz up to it and get themselves killed. You should really show some sign that the door is evil and a monster, such as giving it maybe... something like evil eyes and sharp teeth. ;D
Alright, I go and talk to King when he's laying down on the ground, and I notice the facepic. It's not bad, but if you ever need a facepic don't be afraid to ask someone here to make one for you. Also, when talking with King, he never finishes one of his sentences. It had something to do about the universe of Cave Story, I think.
I go into the Sky Pond area and Save place, and when I exit I am falling down through bare sky. By the way, I know the village is suppose to be in the sky and all, but maybe you could put a warning sign before the little ledge where you could fall off if your not careful.
Speaking of signs, I looked at the one that said where each little place is and all that, such as Resevoir <-- and all that... well, you need to change that and make it more accurate. The resevoir...uh, Sky Pond, is not to the left of the village, it is north or well, up.
The graphics could be worked on more. And I kinda found it cheap to use the original Cave Story maps, even if you changed little things about them. And maybe try editing the bats and all, and making them into new, original monsters...?