This is’nt much of a scene really,
It is more to show the model
Youre on the right track 
You’ll have to work some more on the background scene if you want it to do your model justice.
:yes:the model is cool
Nice model but the background scene is boring and looks like a basic plane with a procedural texture. Try using displacement ot get some shape into the landscape.
Also the pose of the model is very static and boring. Try rigging it and giving it a more dynamic pose.
Including the above, the main point of critique and advice I would give you is, do something about the scene, try turning on the "proportional editing tool to give some character to your landscape.
good job on the model!
well, as this is the ‘focused critique forum’, here is some: you might want to use either the auto smoothing or edge split modifier on the model and the lighting could be improved upon as well, also as others have noted, you might want to add some more variety to the scene and indeed, maybe pose the walker a little as well?
edit: oh, and a specular map would make that model ALOT more realistic/believable! 
PS: i like the design you have used/applied to the ‘head’ of it!
It’s looks cool enough to get commercialised !
It looks like the head is too round, if you remember the AT-AT’s head was blocky but smooth, so let them be edges and not curves. also the feet are too white, id make them as dark as the rest of the AT-AT. (if its a reflection turn that down, the metal in Imp vehicles was very bland with no reflection and a grainy look so the Spec and Ref settings should be at near ZILCH).