First off, yes, it's expensive, but you do get a nice book for your money; hell, it even smells good in a bibliophilic sort of way. The volume itself is a well-bound quality hardcover, though my copy was wedged so tightly into its slipcase that I couldn't get it out without crumpling the dust jacket a little bit. (The jacket, by the way, is excellent: it has no blurb at all, either on the back cover or on the front and back flaps. Perfect.)
Paging through, I was mostly struck by just how strongly the artwork presents in this large (12.9" × 8.5") format; it really does have more impact than in the standard format. The colour looks more or less like it always did; the much-publicised digital "remastering" appears to incorporate only subtle changes, such as making colours more consistent from one panel to the next when they show the same scene, altering background tones for better contrast with foreground objects, and grading some colour fields that were solid in the original. But it still looks like Watchmen; for reference, the biggest single difference I noticed in comparison with my paperback omnibus edition is that Dr. Manhattan is a slightly paler blue than I'm used to (closer to #99CCFF than #66CCFF), and that he's considerably more consistent in colour from panel to panel. I haven't noticed any changes to the actual line art or inking so far.
The extra material in the back (some early sketches, character notes, a few pages of script) is illuminative without being essential. I understand it's all repeated from a late-'80s Graphitti edition, so it's not exclusive to the Absolute edition.
I would not suggest getting this edition just for the extra material or for the re-done colour; both are nice, but I don't think either justifies the high purchase price. I would, however, definitely suggest picking this up if you're the sort of person who wants a good-quality large-format hardcover edition of Watchmen, or if you have a need for something large and heavy and oblong with which to hold doors open or beat small animals to death. Me, I'm happy with it.
(Now if we can just get an edition like this for V For Vendetta...)