Buy this product. It takes material from various OGL sources and combines it with new stuff. The result is a truly modular d20 System product that addresses specific problems with data-driven, sensible solutions. Here are some highlights just from the introduction:
1. A thorough mathematical analysis of the d20 System which forms the basis of the proposed changes found in Trailblazer.
2. A relatively simple system for determining the CRs of customized monsters.
3. The 10-minute rest period, which handily does away with the dreaded "10 Minute Adventuring Day" that so many folks complain about.
4. A simple fix to help speed up the resolution of iterative attacks.
Other chapters deal with Action Points, character creation and character races, a wide-ranging revision of character classes, fixes to spellcasting especially useful for multiclassed casters, a streamlined skill list, modified feats, equipment options, and more.
If you're interested in a more in-depth review, I've gone over the Introduction, Chapter 1, and almost all of Chapter 2 at these links:
Of course, this product isn't perfect. It certainly isn't going to compete on the art front, but Trailblazer isn't about pretty pictures. There are also typos here and there, at least two of them somewhat humorous. These deficiencies might keep Trailblazer from receiving a perfect rating, but they're certainly no reason to avoid this PDF.