The original Star Trek established the template for the franchise and the characters and casting were inspired. Otherwise, it has not aged well because it came along before the advent of the personal computer and digital electronics, which means that a lot of the technology looks rather clunky and old-fashioned. In spite of that, some of the stories from the first and second season are gems. Some are junk, and the third season is a disaster.

The Next Generation has aged much better and is still enjoyable. One episode called The Inner Light is perhaps the best episode of science fiction ever seen on American television. Measure Of A Man is also very good.

Deep Space Nine seems to have more depth than the other Star Treks, even though it is set on a space station that doesn't really go anywhere. The premise of the show allows for a lot of exploration of issues such as religion, politics, war, interpersonal relations, racism...all those details that nag human beings.

I can't get into Discovery at all. Picard is interesting mainly because it has some Next Generation folks as well as Picard himself in it, although his role is very different than in Next Generation; it does, however, get rather dense at times. It would be better if they had found a way to keep Q looking as he did in Next Generation. God-like aliens don't age just because puny humans do. :>)

Strange New Worlds is yet to be seen. It is billed as a prequal to the original series, and hopefully it will capture some of the zeitgeist of the older Treks.