LoTekK, I believe there is more than one level, hence different themes.
There's actually an interesting effect going on which I hadn't been able to pin down in the past. Some of the outlines actually produce banding against the dark background. I guess you could say that where selout is AA against a dark background, whatever you'd call having a tone between the sprite color and the background color wrap all the way around a sprite, is actually banding against a dark background. What you did is great for light backgrounds, because the outline doesn't act as an intermediary. But anywhere I look in this, there are mid to dark backgrounds and
some "selout" would help.
with some light outline coloring on frame 2:

(It doesn't need it as much as later examples but I think it makes him look more dynamic as a sprite and less eh static straight lines. Sort of regains the flair you lost when you took away the white outlines and harkens back to your first image.)
I only added lighter shades to the outline. It should still be okay against lighter backgrounds like the sand waterfalls. Just makes your sprites plump. o3o
also, some other places you might want to look at

Though you could easily get away with not fixing it and still have a beautiful game. You mentioned time constraints and this is pretty low priority if you have new content to make. But if you have time I would lovelovelove to see some going-over of the outlines. Anyway, very handsome!