Well, the demons lack of emotions and personality, yeah, sure the’re demons and they are evil, but you are only focusing on only making them look evil, you are not focusing in the sin that the demon represent, making them generic demons, if someone saw these illustrations without the tittle names, I’m pretty sure that they would have a hard time telling which sin is which.
Your mistakes are in the body gestures and facial expressions, for example, pride, his design is fine, but his posse is not, he does’nt look proud at all, he looks like has no clue of what’s going on, his face should be looking happy, because he should be proud, but he is pissed instead.
Sloth, is resting is arms on his knees, but that’s actually not lazy enougth too be called a sloth, he is too uptigth.
I could go like this withe rest,so, my advice is, that, next time, you should find a posse and a facial emotion that communicates the story that you wanna tell with the character.
1