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 
Dr Who’s visual continuity on the other hand is pretty strong when bringing back old creatures. Daleks still look like they did in 1965, the Sontarians as they did in 1973, the Zygons as they did in 1975, etc. The only race that got a major change was the Cybermen which was explained by being an alternative universe version. Even they eventually cycled round to their original 1966 look by the end of Capaldis era.
I mean… not that much. Daleks have gone through three redesigns just since the show went back. Sontarans went from the world’s most unconvincing rubber masks to makeup. And how many eyes do Silurians have-- two, or three?