I personally hate how Klingons were depicted TNG+. Buncha unbathed Space Vikings so pathologically stupid that it breaks suspension of disbelief that these morons ever managed to evolve beyond the Stone Age, let alone develop FTL travel and build an interstellar empire.
This is the correct opinion. I wish they stayed like they were in the movies. The Undiscovered Country even showed an intellectual side of the Klingon people that I don’t think was ever explored in any of the TV series afterwards.
TUC probably had the most complex, nuanced take on the Klingons. Unfortunately, that was the last time those Klingons were featured.
Not just Klingon culture though, in particular Worf as a character became worse the longer he existed. At the start of TNG, Worf claims that Klingon culture is completely alien to him, having been raised by humans. I’m not sure how early it started, but at some point the writers decided to make it Worf’s one goal in life to be the most Klingon a Klingon could be. This caused more and more episodes to be fully dedicated to developing Worf’s Klingon ancestry.
I recall Worf being in “I am Klingon, hear me roar!” mode right from the get-go. This was greatly disappointing to me, 'cause there was plenty of opportunity to explore the “nature vs. nurture” debate with the character, and it all went to waste.