Very surprised by this trade. We need a big more than we need shoot first PG but I doubt that Al gives us more than Kemba. I guess if you look at this in terms of replacement value meaning how does Horford compare to the big who isn't going to play and how does Kemba compare to Smart, Pritchard, or who ever ends up replacing him in the line up, maybe Al is a bigger upgrade to our bigs than losing Kemba is a downgrade to our guards.
I do like taking the chance on a young big who has put up 20/20 games in the NBA. I have no feel for what his ceiling is but that is a good chance to take. It also does save us some money, both in terms of Horford's contract and that Brown will make less than the 16th pick. That will likely help us sign Fournier and maybe do some other moves with the TPEs.
So the deal is really Kemba, 16th for Horford, Brown and something. The problem is we don't know what the "something" is and may never be able to equate it exactly.