I won't go off on the normal tirade about how The Simpsons is crappier that it used to be like some sentimental fool. That doesn't help anyone. Even season 17 episodes I see again now I enjoy a lot more. Really, they just need time to age. But I do think Al has both done bad and good for the show. He seems to have a very literal, cold, business mind, which I'm sure has hurt the creativity of the series immensely. Just read an interview with him, or hear his voice, or look in his slightly guilty eyes :)
I'm one who dearly misses the crude artwork of it in its earlier forms, and when dialogue felt like it wasn't just said and then slapped in a timecode. But like any job, he can keep things under budget and well-oiled, so he gets to keep his post. In this way, he probably wasn't the best choice for the show from season 13 onward, though maybe he was. We can't really know. As a society begins to crumble, so must its artistry. That's the closest guarded secret of the television universe, and I bet Al's in on it. But once all this 2012 nonsense is behind us, I think some cultural dynamite will go off.