There is more "depth" in those early ones. More extras, sounds and chatter in the background, which gave the ship a more realistic feel.
And crewmen (and women) aren't just walking the corridors, they are doing things like repairing conduits, replacing piping, and going up Jefferies' tubes. The ship seems full and you could honestly get a sense that there are 430 souls on board, not just the handful of extras that we see in later seasons, TNG and VOY.
Also, the turbolifts has double doors -- double doors! -- inner and outer, wow. That goes away quickly to save time, I suppose, and are never seen again in any
Trek.
Emphasis mine
There are only three first-rate episodes in season two - "Amok Time" and "The Doomsday Machine," and "Mirror, Mirror." "Journey To Babel" rates a "B" at best.
Out of all the second-season episodes, "The Doomsday Machine" is the closest to the feel and look of season one in terms of storytelling, characterization, and production (the lighting is even close to the early first-season episodes).
Emphasis mine
The show is not their yet, and many of the eps are just ssssllllloooowww.
Spock isn't fully online yet, with odd aberrations; Kirk is a little too laid back.
Some of the season is just too soap-opera in space.
Kirk is hardly laid back in the first season; he's as serious as a rip in a space suit. He's more laid back and humorous towards the end of season one and for the rest of the series. In those early episodes, he was very much like Horatio Hornblower, someone who internalizes everything and beats himself up over every little decision.
Shatner insisted as time went on the "lighten-up" the character of Kirk, give him a sense of humor and wonder about everything. A good choice since Kirk needs to be a counterpoint to Spock's logic, but in the first-season he is not laid back and is the most for-the-uniform than the rest of the series. I'd even say that the more serious, military-minded Kirk comes back in TMP and TWOK.
As for the first season being soap opera, it's not. Space opera to an extent but that season is the most serious, considered adult drama of all
Trek.