I'm not a Trekkie, not by a long shot. But, I did like the the original series with Spock, Kirk and McCoy, there was a "rough around the edges" quality that has not been duplicated. I recently began to watch Enterprise on the Sci-Fi channel for the first time and I was very pleasantly surprised at how well written and acted this series is. I did see some of the New Generation back in the late 80's , but to be frank it was stiffly-acted at times, too politically correct, the inside of the ship looked more like a corporate office than a spaceship, all the 80's New Age crap had somehow been written into the scripts. The irreverant, womanizing (by today's standards a saint) Kirk was replaced by an aging Frenchman with an English accent who didn't like his daddy nor kids, the old trinity of Spock, McCoy and Kirk was replaced by a woman shrink and a yes man who went out of his way to say he wasn't a yes man. I always thought that the Kirk persona was split into three with The New Generation, the old guy represented logic, the shrink was the wisdom and insight and the yes-man was the "crude" part of Kirk (skirt chasing swashbuckler.) But I find Enterprise refreshing, the picture quality and effects are very good and the story line keeps you interested. Funny I was never interested in Star Trek after the 80's series, but Enterprise has piqued my interest all over again.
Ok here is my opinion on this subject:
The Original Series:
It was cool, and innovative and the characters were classic, but many of the episodes don't stand the test of time. Too much hippie stuff ruined many of the episodes. The movies were great, most notably STII, IV, and VI
Next Generation:
The characters grew on you, it had its moments, most notably with the Borg and Q, but it was too touchy feely and politically correct. Most of the episodes were a bore, but the movies were enjoyable, most notably First Contact.
Deep Space Nine:
Now this was a great show. It started out slow but really picked up momentum with the introduction of the Dominion and Worf. The characters were great and the stupid episodes were kept to a minimum, with the exception of the religion ones most of which were stupid, especially the towards the end of the final show.
Voyager:
Started off good, but didn't really pick up until 7 of 9 was introduced. The Borg episodes were stellar and Janeway was great. The final episode was really cool but seemed to end too soon. Overal this ties a close second to DS9 as being the best Star Trek series, IMO.
Enterprise
The first season was nearly unwatchable due to bad acting and poor scripting. Season 2 got better and Season 3 was the BEST, infact it was one of the best seasons of any Star Trek Show IMO. Season 4 was a half abortion due to budget cuts and show cancellations. It had one of the worst final episodes of any shows in TV history IMO. The plot fell apart, cameos of Riker and Troy were missplaced and it was just pure cheese and killing the shows best character (Trip) was a huge mistake. Enterprise shouldn't have been canceled, but fans didn't support it until they heard Paramount was pulling the plug.
Well thats my take on the different Star Trek series and here is hoping for a new show in the new feature.