It's interesting on Big Al's defense, looking at the numbers on
82games.com. When he's used as a power forward, his defense looks pretty decent; he's holding opposing players to a 46.9% fg%, and his opponent's PER is 15.9, which isn't bad at all. He holds his man to per-48 averages of 18.6 points and 9.9 rebounds. Those aren't spectacular numbers, but in terms of defense, that's probably above-average.
The problem is that the Twolves use Big Al primarily as a center, where his numbers are pretty bad. Opposing players shoot 56.1% against Big Al from the center position, and he is giving up 15.5 rebounds per 48 minutes (and pulling down 15.1, which suggests that as a center, Big Al is actually getting outrebounded.) The scoring numbers aren't so bad -- 18.1 points per 48 -- but the PER is terrible: 20.8.
As always, these numbers are subject to the usual flaws; just because an opposing center puts up big stats when Big Al was in the game does not necessarily imply it was his fault. A lot comes down to defense scheme, and I'm not sure how closely 82games.com scrutinizes actual matchups to make sure these numbers are accurate. Still, the above would suggest that Big Al has a long way to go before becoming an adequate defensive center, which is probably to be expected since it's not his most natural position.