Point well taken
Well, since fantasy occupies 95% of MY reading, i guess i am a bit biased. And about the sequels not being as good as the originals written by the inventor of the series - that is always the case.
The first 5 books of the Chronicles of Amber were written masterfully by Zelazny, the next 5 by the Amber Corporation (whatever that is, i just saw it on my US copy of the book).. They are worlds apart. While in the first 5 you really don't know what's happening, who to like and who to view as the villain, things constantly change and to top it off, you really see just how smart the leading character is. The book is not a "superhero bashes bad guys" thing, ti's much more complex and shows the character as a vulnerable and believable person one could relate to.. Not some all-powerful Mary Sue
The next 5 books are just a cheap imitation, trying to do what was done by Zelazny in basically the same way but under different circumstances. And they failed..
And further more, they completely ruined the universe of the books with making drastic changes (such as adding the Logrus and making it and the Pattern sentient - can you say CORN?) That's why before Robert Jordan was diagnosed with Amylidosis he had stated that no one will ever have the chance to write in his universe after he passes away.. He sort of started having second thoughts now, but that's a different story.