The very definition of hit or miss.
The comic book sections are usually pretty good, but the prose sections that intermingle throughout (due to the idea of it being a history of the League) are really all over the place. The Shakespeare bit is too blatant and the Beat novel is un-fucking-readable, but many other bits are various degrees of fun... depending on the reader's mood. It says something, though, that one of the best prose pieces in the book, Les Hommes Mysterieux, about when the League fought their French counterparts, is immensely frustrating despite everything good about it because one can't help wondering why the hell it wasn't done as a comic.
The Orwellian Tijuana bible, on the other hand, was pure genius.
Moore is, as always, a great writer, but too much of this book feels like a writing exercise instead of a finished product for us to read. Plus, the 3-D section at the end is rather ill-conceived due to A) 3-D glasses that wouldn't fit over my big honkin' Jew nose, and B) so much going on, and so much dialogue, that it becomes a real strain on the eyes.
Don't get the wrong idea, though, it is an entertaining book at many points, but pales in comparison to the first two volumes. Borrow it or find it cheap, I would not recommend shelling out $20-$30 for it (I didn't).