Ultimate Equipment sets as...well, an "ultimate" source for every type of Pathfinder item imaginable. But it doesn't seem to fully live up to the name.
Positive: New formatting
Mixed: Artwork, Treasure Tables
Bad: Lack of new items
On the positive side, the organization and new formatting is pretty slick. It's easy to skim, items stand out and the most important information is learned at a glance. The colored tabs on the side are also a nice addition to help you quickly orient yourself within a chapter. For instance, the Arms and Armor chapter breaks itself down into Armor, Weapons, and Special Materials. They aren't usable to open up to a particular section with the book closed (like a true tab or thumb index would be, the color does not cover the edge of the paper and the pages aren't aligned well) but if you are thumbing through they do help. I expect to see subsequent books make use of the some of the formatting here (especially the tabs).
Most things however are somewhat a mixed bag. The artwork is good; previous books have put a whole bunch of different items in one picture, and if something caught your eye you had to dig to find the relevant text. In Ultimate Equipment however, pictures always appear right inside the item block, so if something catches your eye you need look no further. However, because of the new format, the pictures are sometimes scaled down so they fit (I guess the block format has some bad sides as well). Additionally a good deal of the artwork is repeats from previous books. One final note on the artwork: where is the picture for weapon enhancements? Not all of them are best captured in a picture, but I'd love to see a brilliant energy or corrosive weapon.
Another example is the new treasure generation tables. Some of them I know will help me personally offer my players a more diverse treasure palette. But others are really just fixes for what should have been included in the Core Rulebook years ago--I'm looking at you potion and scroll spell tables!
On the bad side (and this is a pretty big bad side) there isn't a wide array of new magic items. Nothing in the book really popped out as new. It seems most of the new items are stuffed in the alchemy section, as well as a few new animals (which still aren't really new, most just have been priced).
Others have dinged Ultimate Equipment for lack of completeness and for containing errors. I haven't investigated these claims, but I agree that errors should definitely have been fixed.
In the end, I don't see many reasons for GMs to get this book, and even less so for players. The treasure tables are nice but some of them should have been included in the Core Rulebook to begin with. For players, I see even less reason to pick up a copy, unless they are really focused on alchemy.
Looking into the future towards Ultimate Equipment 2, I think Paizo should focus on bringing in some of the things others thought was missing from UE1, presenting more new artwork, but perhaps most importantly adding more original items of all flavors.
