The basic idea behind Star Wars is an epic conflict between good and evil, and the basic idea behind Star Trek is exploration. The idea of an epic conflict between good and evil works well for the movies, which allows the story to focus on the climactic moments without getting bogged down by the details of everyday life. The idea of exploration works well for a TV show, because it allows for a wide variety of stories without having to worry about story arcs or what to do between climactic moments.
Like Star Wars, some science fiction TV shows have been more about epic conflicts between good and evil than about exploration, but they usually haven't been as good as Star Trek.
One example is the original Battlestar Galactica. The Cylons have destroyed the 12 colonies of humanity, and they are fighting against the evil Cylons for their very survival. But too many episodes of the original Battlestar Galactica failed to focus on this conflict, and when I watched it on TV as a kid, I didn't really understand what the show was about. I simply knew that it was a science fiction show about people on a spaceship. In contrast, I easily understood what both Star Wars and Star Trek were about, and I was familiar with both before Battlestar Galactica came on TV.
Another example is Andromeda. Also created by Gene Roddenberry, the show superficially resembles Star Trek. Both are about the captain and crew of an interstellar spaceship. But this show mainly focused on the conflict between good and evil, particularly in the form of the Magog and their evil god from some other dimension. The fourth season ended with a climactic conflict with the Magog, and then the last season lost its way, and the show was no longer as good as it used to be.
The conflict between good and evil has been a staple on some other science fiction TV shows, but to continue coming out with good stories, they have had to share the focus with exploration or political intrigue. Star Gate SG-1 has combined the conflict between good and evil with exploration of the galaxy, and it's now one of the longest running science fiction shows on TV. The new Battlestar Galactica began with the same conflict as the old series but has managed to put more wrinkles into it and make it less black and white. The new season will actually be playing out a different kind of conflict than the original series ever dealt with. Some Cylons have had second thoughts about destroying humanity, managed to become the new Cylon leaders, and believe their mission is now to serve humanity, much like the Humanoids in Jack Williamson's novel. Doctor Who has had various conflicts between good and evil, especially with the Daleks, but it has been its heavy emphasis on exploration that has made it the longest running science fiction show on TV.
To sum up, I think the idea behind Star Trek is a great one for TV, and the various Star Trek series have handled it well, especially the original series and Voyager. Some series, such as DS9 and Enterprise, have focused more on the conflict between good and evil, but even these have had exploration to fall back on, because the main mission of Star Trek crews has been peaceful exploration, not war. The idea behind Star Wars works best in the movies or in TV shows with limited durations, but something more is needed to keep a TV show going year after year. Star Wars makes for better movies than Star Trek, but Star Trek has more of what it takes to last as a successful TV series.
