I grew up on Asterix albums in the 1970s, mostly in English, but sometimes had to settle for French -- they (and Tintin) were the ubiquitous reading of my youth. I've been trying to find a reasonably priced copy of this guide to the series for more than a decade, so I was super-excited when I finally found one and cracked it open. I suppose, then, the first word that came to mind is "underwhelming."
First of all, the design of the book is not great. When I think of an Asterix album, I think of a glorious full-color feast, and so I just wasn't prepared for this almost entirely black and white book (there's a tiny color insert in the middle). Once I got past that, the clunky layout and poor typography bothered me throughout. It's got huge margins and large text throughout, and it's just not very elegantly designed (unlike the various similar Tintin books that have come out over the years.)
The content is a pretty mixed grab bag. There's a nice short history of how Goscinny and Uderzo's creative partnership came to be, and the origins of Asterix. The author had ample access to Uderzo, and so there is plenty of straight-from-the-horse's-mouth stuff here, and the book is especially strong in points in explaining how the humor of the stories worked. There's a reasonably interesting section about the English translator team, and how they had to rework all the regional jokes and French wordplay into something with a similar flavor and cadence in English. The book-by-book summaries aren't that interesting, although I hadn't known that the English translations came out in a different order than the original French.
All in all, if you're an Asterix completist, it's probably got enough tidbits to make it worth reading, but I wouldn't go to huge lengths to track it down. If you're a casual Asterix fan, it's definitely not worth it.