This is a great book, literally as well as figuratively speaking. It weighs in at about 19lbs (according to my unreliable scales), so you'll want to be home when it arrives...picking it up at a depot could be a painful exercise! It consists of two lovely hardback books (glossy pages) encased in a high-quality cardboard cover. The quality of the books partly explains why the price is so high.
The book contains enough Far Side cartoons to keep you going for months, well, days if you're a real fan. I wasn't really impressed by Steve Martin's foreword, but the introductions to the chapters are good. The bit I like best (apart from the cartoons themselves) are the letters to the editor that are included next to some of the panels..absolutely brilliant!
All this makes the steep price tag well worth it. If you're a fan, buy it now! If you know any real fans, buy it for them and they'll love you forever.
Oh yes, downsides. Well, as the previous reviewer says, it's too heavy/bulky to take to the loo or read in bed comfortably. It's also a tad difficult to read on public transport. If you're giving it to somebody else beware: there's a white bit with the price on it printed on the top of the case (inside the plastic wrapper). I haven't quite worked out how to camouflage that yet. On the other hand, it's a good (although not too subtle) way to show how generous you've been (especially as it says £100, and you'll get it for £70 here at Amazon)