Voyager had some really cool episodes caught in the midst of a lot of really mediocre to bad ones.
The nature of the show's storyline gave them the opportunity to visit some really cool concepts. It kind of went back to the roots of Star Trek, which was originally a show about exploring the universe and stumbling on some really weird things along the way. Later seasons of TNG and all of DS9 really dropped that concept and focused on other things (like sitting around tables having long talks about diplomacy, then going out and shooting stuff).