When I first heard about Voyager I thought it was the dumbest idea yet -- why do a series where Star Trek meets Lost In Space? This belief kept me from ever catching the show while it was on. Then I started watching the dvds and I was hooked.
Why do I like it? First and foremost, the characters are interesting, diverse, and I came to care about them. Second, Voyager is the most Star Trek-like series in a long while and feels like it has the (non-corporeal) guidance of Gene Roddenberry. The stories got better and better, without trying to compete with Battlestar Galactica or some other series. It is a great show, period.