We're loving our king GhostBed. It's a good level of firmness, but not uncomfortably so. I also didn't notice much of a breaking in period before I felt it was comfortable. Overall, I'm pleased with the comfort for the low cost of the mattress.
My wife and I were sleeping on an older style spring mattress, which after a few years was finally breaking down. The GhostBed is a lot stiffer than I anticipated. My wife on the other hand loves it.