I've only visited the Botanical Gardens once, during the very early spring, as part of a high school environmental club. It may just have been that we were with a large group; or it might have been the time of year; but there really wasn't all that much in the Botanical Gardens.
I have seen some beautiful flowers and amazing trees (for instance, at the arboretum in the South Chagrin Metroparks Reservation), and I was expecting similar when I came to the Botanical Gardens. There were some very pretty trees and flowers, but not many, and none really breathtaking.
If you like to photograph flowers or plants, this may be a great place for you. There are more than a handful of excellent photo opportunities, and you won't be disappointed. But to the human eye, there isn't really that much to these gardens; they're not very big and, last I saw, not very diverse.
On the other hand, it may be a wonderful place to visit in a season when more flowers are in bloom. I will go again the next time I'm in Cleveland. There is considerable potential in the Botanical Gardens if the space were used well, and I'm cautiously optimistic.