In all these ways, The Gates transform the park. They make you see and feel it differently. That's art enough for me.
I didn't see The Gates, obviously, but I have a pretty inclusive view of what is art and what is not, and I might well have viewed them thusly. Maybe we can get the creators of The Gates to come to Buffalo and do something similar in one of our parks. (If we have any parks left, that is. Ye Gods.)
(Although, I have to admit, that as well-received as The Gates were, I'd much rather lay my eyes upon these Gates. A Elbereth!)