The assembly was not difficult but was complicated by the poor quality of the product and some flaws:
-Two of the legs are crooked. And when we convert it to bed, one of the legs remains floating.  
-A set of nuts was missing and we have to get them in a hardware store.
-It makes strange noises sometimes, and the mechanism to turn it into a bed is very noisy. 

As for the rest, the sofa is nice in design and color. We found it comfortable (better with some pillows). 
The quality is not perfect but seems ok for the price.