It's interesting to see in this thread the split between TOS trekkers and a STTNG trekkers. I was always more of a TOS person myself: I think the creative tension that the networks put on Gene by making him "dumb it down" actually made for better, sharper analysis of the sci-fi involved. TNG seemed to meander a bit. But that's me.
What I find interesting about looking at the shows from decades later is the way the topics were addressed. Things like the episode where Daystom's M-9 computer took over the Enterprise and basically was a smart machine with a weapon -- we seemed to have come down on the side of that being okay, at least for now. But back then there were a lot of very important questions raised -- questions that are still valid. Or the Darmok episode, where the culture spoke only in metaphor. That still twists my noodle because that's all any culture really does -- speak in various metaphors. When you're asking a bunch of users from a certain societal niche to tell you what they want, not only is their jargon going to be unique, but the way they compare things and discuss things are too. (Insert Wittgenstein discussion).
Taking a short dramatic format and making a bunch of pimply-faced teenagers start thinking about what's important in their lives is an awesomely good thing. Let's hope Trek keeps doing that for years to come.