We have a '04 Suburban, and an '02 Avalanche before that, so I'm very familiar with the Suburban and large GM truck in general seats. When I test drove the Acadia, I wasn't sure what to expect in that aspect but wasn't totally dismayed. Everything folds flat easily, which is a HUGE advantage over the full-size GM suv's, but as has been said before, the rear seats do feel low, at least to a lot of people. The seat design itself is not uncomfortable, but back to back with something like a Tahoe, for instance, you get the same support but feel like you're down in a hole a bit in a Lambda crossover back there or that you have the settings wrong and too low. As compared to being higher, and your legs having a more natural downward spread in the larger trucks.
Now, again, it wasn't really objectionable, and if I wasn't familiar with the Suburban, I might not have noticed as much, but it's still something to consider. It bothers some people, and others could care less. To me, the Lambdas are so strong in most every aspect, I could probably overlook it, but I'd have to give the rear seats another try out and a longer test to see.
As for the Enclave, as was said, nothing really different aside from some cushioning aspects, and the same semi low rear height.