This is very cool, however I dislike the generic silhouette of the guy. I am aware that it is there to provide a sense of scale but it lacks character and distracts from the building in the background (the sharp contrast between it and the bright building draw attention towards it) (also it is very organic in shape leading one to believe that it lacks clothing). I think this piece may also need something in the far background (behind the building) like mountains or a large city or forest. Other than those bits this is fantastic.
Ooh, that mech makes much more sense and looks very nice. Now the picture seems to have a story to it. It could be a government run power plant guarded by military mechs in case there is an attack on it or something. Very nice addition! And thanks for taking my advice, I honestly didn't expect you to use it but it's cool that you did.