I watched the original series and saw all the TOS films. I have seen almost every episode of The Next Generation, and I have seen all of the TNG films except the last one. I have only seen about a third of Deep Space Nine, and I have never watched a full episode of Voyager. I have never owned a television, so I am slacking on my Star Trek viewing. Perhaps someday the Star Trek videos site will have all the episodes from every series available.
I have gathered that a lot of Star Trek fans do not like Enterprise. But do you really think that every episode of TOS was a winner? Also, I think that if Gene Roddenberry had not been involved with TNG for the first few seasons it would not have lasted as long as it did. I think it started to get good in season 3. Deep Space Nine also took a while to get off the ground.
Off the top of my head, my favorite TOS episodes are “Balance of Terror” and “The Enterprise Incident“. My favorite TNG episodes are “The Best of Both Worlds” (I think just about all the Borg episodes were good), “Yesterday’s Enterprise“, “Booby Trap“, “All Good Things…” and “Parallels“. I also liked “Masks“, although I know most people did not. Nothing wrong with taking risks.
If you are going to jump into “Future Tense”, you should probably watch all the episodes about the Temporal Cold War.
Enterprise does have the same prequel paradox the Star Wars prequel trilogy had: It takes place in an earlier time and all the technology is supposed to be less advanced, yet all the technology looks more advanced.