We saw a noticeable increase in the quality of his pictures with those two lenses. Of course he had upgraded from a 5D to a 5D II body as well. His pictures and the amount of improvement he had with the 21mm is one reason I keep thinking I still want it.
The only negative I read about the 21mm is the distortion. For a landscape lens I would most likely not notice.
The 35mm I have seen many complaints about color fringing. Do you see any noticeable problems with color with the 35mm?