some nice work here dude
just two quick suggestions. try a lil less saturation (bumblebee is like wow glowing
)
second is that although there are shadows imo the some of the images look kinda flat.
on the background i personally use two layers of shadow with the first set at 35% and the second at 55%. whilst with the characters etc i usally have both set at 45%. you have got some awsome work here though. just needs imo a lil more omph to really make it come alive