Not being known for my political correctness, I would probably assume that one never asks a question if he doesn't want to hear the answer. So, to get out of sticking my foot in my mouth, I'd ask him what were his favorite aspects and why. Then ask him "what if..." It's amazing how many times you can see the light bulb go on ".... I never looked at it that way....".
If it was to comment on another architects work, probably be on the same page as Ian. At that point it's all about preference. And, even at that point, even if you point out the errors of their way, it's not likely they would A)admit you were right or B) do anything about it.