Moo has all the perks of Horse Heaven, but without the flaws. It's a massive, sprawling cast of characters, but they're successfully held together by the overarching frame of Moo University, and there aren't so many of them that you get totally confused as to who's who. It has only one animal character, the giant hog Earl, but he's a well written and very likeable creature. It has Smiley's typical warm, pleasant prose, and a bit of the ironic humor. Although a lot of the satire seems kind of outdated, it's interesting nonetheless, and kind of a nice time capsule of its particular moment ('89). It's probably more entertaining to those familiar with the strange inner world of universities, but it's not quite as dorky as, say, David Lodge novels (which I love).
All in all, a warm and pleasant read, if a rather long one.