am I just imagining it or does Aang's face look a little different?
It's because he's older, this happens in a universe where he didn't discover he was the avatar until he was 18 (or 21 depending where you live), and only then he fled, became an ice popsicle and met the others all over 18 (or 21...), and of course the comet took longer to appear, because the one above all of this multiverse so desired.
Well everything I wrote is just a bunch of bullshit, the writer had a better explanation, but I was too lazy to give a fuck at the time.
P.S.: Also our artist has not yet finished Aang's art and some other arts, so he doesn't look as good as Katara for example, but it'll be better in future updates, this was only a demo.