Pretty much exactly the same response as Intrinsic for me. It was great for several years, and then it started killing my back. Maybe I got fatter, maybe it was the mattress, I dunno.
I bought a new one that someone else mentioned a few months ago, figuring I might get another couple of years out of it. It was some Green Tea mattress. It was half the cost of my old one, which was nice, and it feels ok for the first few hours, but if I sleep over five or six hours straight, my back starts to hurt really bad. Again, could be fatness, but I am not that much heavier than when I bought the first one five years ago, and that one instantly fixed my sore back (until it wore out).
One difference I instantly noticed was that the first one I had literally molded to my body like memory foam is supposed to. Eventually that wore out, and now it is just kind of a big foam mattress. This new one doesn't mold itself to my shape either, and I feel like that's why my back is still hurting, because it is just a big foam block too.
So I don't know if it is just that this one is cheaper, or not supportive enough, or something else. But I'd have returned it if there was a feasible way to do so...and if I hadn't tossed my old mattress immediately. Still, for the cost, I'll just suffer through another year or two and then hopefully get another one that works better.