Early episodes were therefore like little films. They were often moody and atmospheric, whereas many TNG episodes felt like they were filmed in an 80s hotel or shopping mall.
Sharp observation. Even as TNG hit its stride somewhere in season 3, there was a tepid air about it--a lack of a living heart. Few stories felt organic/dramatic, but read like a script meeting: just saying words surrounded by Trek-ian sets/costumes.
TOS was aimed at a general audience whereas TNG seemed conceived for the splinter audience of Trek fans.
I would say that is half true, in that TOS was trying to appeal to a general audience (there was no established sci-fi demographic for studios to target as a formula, as would be the case in the 1970s - forward), but TNG used TOS' breakout as a pop culture event to zero in on Trekkers--trying to win that audience first, then appeal to a more sci-fi conditioned culture as it existed in 1987.
TOS was helmed mostly by people in the WWII generation, many of whom actually had served in the military. TNG was made mostly by their kids, college-educated Baby Boomers raised on TV shows.
I have encountered that observation since the early TNG days, as there was a strong view that the TNG reality was not as brutal or consequential as that seen in TOS.
To be clear, it was not the long-abused "Kirk vs Picard" nerd war, or the "Roddenberry waned TNG to be a utopia" dialogue, either. It was a direct judgement about the post 60s / yuppie-esque sociopolitical feeling that would run through TNG, and (eventually) various plots of the sequel series.
Granted, TNG was not a series born during the Cold War, or shaped by people who lived through the Depression and/or participated in WWII. However, the lack of that sort of hyper real life experience should not prevent anyone (in the decades that followed) from creating stronger tales, especially when TOS existed as a template for the fictional universe.
Lastly, TOS episodes, even the bad ones, are memorable. TNG feels for the most part disposable.
I cannot disagree. It makes me think back to TNG, when it turned 20 in 2007; there was hardly a media nod. When TOS reached 20 in 1986, there were official celebrations and a wealth of media (news) coverage / analysis. One was viewed as special...culturally relevant. The other is just "that other Star Trek show."