I am the kind of person who enjoys "big weird" scifi like Stanisław Lem. Stories about trying to relate to and find common ground with something so alien that the prospect of even understanding is basically hopeless. Star Trek usually doesn't do stories that, which makes sense as it often uses alien races as allegories or stand-ins for real-world human relations.
That said- I thought those early Klingons were super weird and scary because they were just so alien. It really made sense thinking about how it took a century before they could get to the events of Star Trek VI, and it made the Khittomer accords feel like so much more of an accomplishment. Like- you made a treaty with WHAT?
And just aesthetically their ships and armor looked like something out of HP Lovecraft or HR Geiger:
This is not to say I dislike how Klingons were portrayed previously, kinda like Mongols in TOS or Vikings in DS9, just that they never felt scary to me. They never felt like warriors. I was never afraid for the gallant crew of the Enterprise D (a science and exploration vessel) going into battle against Klingons. But I really enjoyed the alien-ness Disco tried to go with. Anyone else with me?
EDIT: PEOPLE I SAID WHO'S WITH ME NOT WHO ISN'T CM'ON 
are you talking about Worf's "we don't talk about it with outsiders" line in Trials and Tribble-ations? Because I also think it's ridiculous that people took that line so seriously. It's a little meta joke in a comedic episode that solely exists to celebrate nostalgia for TOS. I don't get how you can take it as serious confirmation that Klingon's appearance changed in universe in that context.
Frankly, I don't get how someone can watch a whole scene and go "well that didn't actually mean anything for the characters that just experienced it". It makes more sense to assume that words have their intended meaning, and that Worf's friends were genuinely shocked to see flat-headed Klingons than it does to pretend Worf, Bashir, and company never actually had that discussion. Like, yeah it's all fake but main characters are supposed to be real people, the situations are supposed to be real to them...