Absolutely terrible. The mattress is about 5" shorter and 3" narrower than my previous mattress, so there's tons of extra room between the mattress and the edges of the bed frame. 

The firmness was excellent at first, but after 6 months,  it's significantly less firm. Now I can feel the box spring underneath when I kneel on the bed. And the box spring was such a bear to assemble! If they'd given me the option, I would've paid extra to have someone assemble it for me.