I think the anatomy could use some work, particularly on the third guy. guy1 has a really round pec, almost like it melded with his deltoid. guy2 has small hands and short arms, and the little '+' signs in all of their chests is kinda strange. what sticks out most to me (in all three but especially guys2&3) is the connection between the neck/torso/shoulders. make sure you're aware of the relationship between the deltoid and trapezius, as well as the placement of the collar bones and muscles of the neck. guy3 has a really tiny head and his jaw doesn't reach toward his ear far enough, which I guess you could write off to him being an alien or whatever but it still looks odd. his ear is also crowding the face. his pectoral seems to stretch back too far rather than slope up toward the deltoid and the blue arm is really large, especially the shoulder.