Mouseguard has amazing presentation and terrible rules. The original Vampire: The Masquerade is another example; incredible presentation, horrible rules. GURPS is always very readable and feels logical but plays horribly and it quickly become apparent that feeling logical isn't the same as well designed.
I'm struggling to think of a book with terrible presentation but good rules, unless 1e AD&D counts. I would put 4e D&D possibly in that category as well, though the rules didn't appeal to me, I think they did appeal to some, but the text was bone dry and dull and the art was maybe the low point in D&D history.