Very narrowminded view really. There was 20 years between the end of Nemesis and season 3. People change during so much time. Besides, Worf at the end of DS9 was a different Worf already than we first met in TNG.
As Mr. Laser Beam states, Worf wasn't raised by Klingons. His take on their culture is from textbooks mostly, making him in a way a textbook Klingon. He experienced Klingon culture first hand only a handful of times growing up. He basically learned everything from books. Ofcourse he has a very rigid, idolized view of Klingons and their culture. By the 24th century, the hardline followers of the Way of Kahless had dwindled. The Way of the Warrior become the way of the ruthless conqueror with less honor towards his enemies and fellow Klingons than Kahless himself tried to teach them.
The Worf that begins to develop over the years, especially late TNG and during DS9 is a more balanced character already, learning that things are not as he always thought they were.
It's a pity most fans will never experience the Worf we saw in the novels set after DS9. As a character he grew a lot, and became quite more nuanced.
