There are many characters in the series, but I never felt lost when it came to who is who. Every character that was important had his or her own distinct voice and unique personality. I equally rooted for the main characters, Kendra and Seth, and the minor characters that came along. My favorite character would probably be Tanu, the Samoan potion master.
Each novel had a really great adventure to follow, along with plenty of side stories that tied the entire plot together at the end of each book. Book 1 (Fablehaven) just barely wet my appetite for the adventure. Books 2-4 (Rise of the Evening Star, Grip of the Shadow Plague, and Secrets of the Dragon Sanctuary) had me biting my finger nails in anticipation of what would happen next. Book 5 (Keys to the Demon Prison) made me laugh, cry, cheer, and boo over and over again. It had my attention up to the very last word.
This is a great series. Anyone that is a fan of Potter-like fantasy will thoroughly enjoy Fablehaven. Brandon Mull did an excellent job with the entire project. At the end of the last book, he confirmed that it was the last book of the series, but did not rule out returning to the same world in a possible future series later on. Although the predicted series would probably not feature Seth and Kendra, I'm hoping he does one day start another adventure set there.