JLA: One Million as well as other parts of the JLA run - especially Mageddon. Meandered about, plot-wise and suffered from terrible art. Didn't outright despise it, wouldn't personally attack the creators, but didn't love it either.
Apart from that, it's all good. I mean, nobody's flawless, but Morrison does a pretty near-perfect job with the rest of his writing. As with Ennis, Gaiman or Ellis, you can tell that he puts a lot of thought into his work while also making it thought-provoking.