Love this sofa. Assembly was pretty straight forward ... just make sure you leave the bolts loose until you've assembled the whole thing, and then tighten them all in 2 or three rounds.
First time my husband and I sat on this, it was immediately clear that it is SOOOOOO comfortable on the back.  It is firm, no sagging at all, and the depth of the seat is perfectly positioned so that the back actually supports you ... allows for a relaxed upright posture that relieves pressure on the torso and hips. We were so delighted with it we bought the matching chair, and also the blue sofa and chair. Love both colors!  All 4 pieces are a mix-and-match in our living room.