Check www.projectaon.org for online copies of the original books. The new ones coming out are revisions of these originals.
The RPG is simply a guide to playing in the vast world explored by the books, built heavily upon the d20 rule system. Magic isn't too heavy in this world. There is not a vast index of monsters to fight. Much of what makes this world interesting are the character classes.
The ultimate class is the Kai Lord, which at level 20 will have close to 100 class abilities at his command. They are the chosen of the god of good, Kai.
Other warrior classes include the Vakeros (known for bluesteel armor and weapons), Telchoi (desert warriors), Bor Gunners (dwarves with firearms), and Sommerlund Knights.
Magic-using classes include the Brotherhood of the Crystal Star, Dessi Mage, Herbalish (think good druid), Cener (think bad druid), and Sage of Lyris.
And at the site www.towerofthesun.com, you can find absolute scads of fan-created material, ranging from epic level Kai to artwork to stories and entire new classes. (Yeah, shameless plug).
Even without the RPG, it is a great fantasy world to explore through the books. With the RPG, it makes it more fun. Now that the whole line is beign rereleased, well, needless to say most of us who have known of the series for 20+ years are extremely excited.
KL (better known as KHFA)