First video
in fact... you should try to add dead trees around, maybe a graveyard... and a forest... or more houses... because we can see that this is a single plane.
If you are in maya you also should try the fur system to get a nice grass without loosing your time. But if you don't come close to the ground... a bump map with a nice texture can do the job.
And the sky is hard to make a realistic one... you have to find a good HDR image of a sky and do a sphere with the texture in (in the mental ray indirect lights settings there's a way to create it and it also give a kind of.. light)
Second video
the arms are supposed to be flying or attached to somebody? if they are supposed to be flying its a nice shot but you should try to make something like... fog coming out of the arms like if it was a ghost (personal idea) with particles or something like that
hope my comments help!
and I have one question
Are you studying in 3D or in cinema?
I can't wait to see more of your project =)
have fun
Maya modeler - current project Avatar - purplemikey