This new version of the Unearthed Arcana is very different in content from the multitude of other d20 supplements out there. Unlike so many of these others, it's not just another collection of new feats, skills, prestige classes etc. What it is is a range of ideas and options, both additions and alternatives to the existing rules, with which to customise characters and campaigns.
To offer some examples: in common with such game systems as White Wolf and GURPS, D&D has now added the idea of "character flaws" as a counterpart to feats (take a flaw - get an extra feat), as well as "traits" which can be taken in addition to feats/flaws with each feat containing closely related game benefits and hindrances. There are pages on variant character classes and races to tailor them to suit most concepts (aquatic dwarves, warrior sorcerors etc) while retaining the balance between their abilities, as well as offering variant spell casting systems. Some of the thinking behind the creation of the rules is included, as well as sidebars with brief comments describing house rules that some people have used. Extra rules options have been added to cover such things as contacts, reputation, sanity, action points, wounds and vitality - things that were introduced in other d20 setting and now brought together for easy access.
It's perhaps not the ideal book for the newcomer to D&D, but for the more experienced DM or player it's full of interesting and (generally) useful ideas, some of which might be just what you needed.