The sky doesn't match the general lighting. You have a dark brooding sky but strong shadows on the building suggesting a bright sunny day. Also the sepia is a bit overdone for my taste, to me it would look better with the saturation wound back about 50%
I agree about the image being unlevel and the dark clouds at the top. Maybe try to tone them down and try a subtle vignette instead? I think it detracts too much from the image when it's only on a small part of the sky and rest of the clouds are much brighter, but I think I see what you were going for.
Also, the Washington Monument being so bright, really draws my eye right to it. Maybe try to do some local adjustments to bring it down to the building? The only other thing I might comment on is the really large depth of field, I would almost expect the trees in the foreground to be at least a little blurred to help draw more focus to the building, only slightly distracting. Not a big deal.
Other than that I like it, the aged dark sepia tone works well for my eyes.