Taken on it’s own terms, as originally intended, TOS is great. And as a television show, it still is. But seen in the light of Trek’s ever-changing, retcon-happy “big picture”, were the adventures of Kirk and Spock’s Enterprise that amazing? Or were they just another ship and crew among many?
Everything fans long-assumed were “firsts” in TOS and the old movies were pre-empted by Captain Archer’s Enterprise, 100 years previously. Time travel, saving the world, meeting new species, having a Vulcan science officer, escaping Rura Penthe… all old hat by Kirk’s time.
Recent "evidence" suggests the Enterprise in TOS was a smaller, Voyager -style ship next to larger (and unseen until Star Trek (2009)) Kelvin and Kelvin kitbash-type starships. It’s possible those ships, in service in alternate-2258, were retired by 2265-Prime, but unlikely.
So, we’re left with adventures that followed in the footsteps of the NX-01 crew, a USS Enterprise that wasn’t Starfleet’s biggest (although it could have still been the most advanced) and a Captain Kirk in the shadow of the Enterprise-captaining, Federation-founding Jonathan Archer.
In light of all that, are they still great?