Nice set. I agree with a few others, the first image is my favorite. I've been getting into long exposures as of late. Mainly using a B+W ND 10 stop and also stacking it with another 3 stop ND for even longer exposures.
Really nice serices, especailly that first one with that vignetting that you have going on. These are really perfect architectural photos, that really bring out the form, light contrasts and such of the buildings and eliminate any other potential distractions. I've always felt that more often than not, good photography is all about simplifying the subject to it's essence and these really do that.