I watched every one of the series in first run as long as I could. The times that I missed episodes and Enterprise's last seasons were not by choice, but due to changes in financial situations (usually for the worst). There was never a time that I stopped watching any Star Trek series due to being disappointed or bored with them. I can't say that about other television programs.
I've long had the opinion that science fiction is the most theatrical form of visual presentation because of its artificiality, and I think Star Trek has used that theatrical sense consistently better than anyone else.