The trees are maybe a tad bit overdone where I can tell it is HDR, but I still really like the image. Great building and I like that you didn't go way overboard. I like more natural HDR.
They just seem to stick off of the background somehow. I seem to always have this happen with trees. They are also just a little blurry. I don't even know if it is overprocessing, but I see this alot in HDR.
Nice shot, and I don't think it's overdone. HDRs often seem to be short on contrast and this might benefit from a little bit more. You can do that by boosting the strength or white-point controls in Photomatix (if that's what you use) or do it with your photo software.
I agree with the above comments. I'm not a big fan of HDR as I've often seen it done, but yours is excellent. BTW, the vignetting doesn't hurt this one at all.
looks awesome to me... if anything, you could have probably even pushed it just a hair more but if you're going for a natural looking hdr, i'd say you got it down just right.