That's a pretty bright scene. The EXIF data shows the photo was shot at f8, 1/250, Pattern metering and 0 exposure bias. It looks like about 1 stop over exposed. Have you tried another lens on the same scene? Your first photo was taken at f9 and 1/320 sec.
As to your vignetting, I think the Tiffen filters are pretty thick. While I think this particular scene can benefit from a UV filter you should get a thinner filter designed for wide angle lenses. That should help. I would probably advise against using any filter with this lens.