Let me start by saying this thing is HEAVY!  I was amazed with the weight of the package upon arrival.
The shelves and sides are very sturdy.  Check your measurements before you order - I did not and this bookcase was larger than I expected.  My only complain is the backing.  It's a cheap, shiny cardboard and required an obscene number of tacks to secure.  I'm not sure I'll even be using it.  Other than that, it's a great bookcase.  You'll need help moving it (unless you have a hand truck) but it's possible for one person to assemble.