As of 12/09, this was the latest Guatemala guide when my wife and I traveled there for 3 weeks.
The too little: Businesses are evolving, coming and going so quickly there were many cases of information being out of date already.
The too much: Guatemala isn't that big of a place, so to fill a whole book's worth, they pack in a lot of very small, out of the way, and minor locations/events/details. This is awesome if you're going to be travelling a long time and/or going way off the beaten path. In our 3 weeks of mad travelling, we still didn't even hit all of the 'highlights', and had to wade through a lot of stuff of little relevance to us.
I bought this because we already had a travel guide (about the same size) that covered all of Central America, and I thought that the Guatemala section might be too sparse. Turns out it would probably have been just right.