It genuinely could be any of those, and I agree, it feels 'flat'. That's exactly the word that came to mind.
I'll try throwing in some more shading. I was trying to sort of keep the shadow mild to really emphasize the light vs dark, but that might be an issue.
I'm hoping to avoid entirely redrawing the poses. I went through probably four different sets before I settled on these ones and it'd suck to have to start completely over. But if I must, so be it.
Any suggestions? I do want to keep sort of non-dramatic poses. I was going for just standing sort of casually with their backs to each other and just kind of glancing back a little bit. You know, like when you want to look back at someone but don't want them to notice? lol.