YOur enviros have got a nice overall mood, which is good. Be careful with your characters; in some of them the feet don't seem to bo touching the floor. Also, watch out the proportions: in the frog one, for example, the arms look a bit too thick, esp. on the shoulder area. Also, a more crouched legs would have made a more natural position,seeing that frogs don't stand on the tips of their toes but on the whole "palm", like us. Anyway, you've got some cool work. Keep it up!