You ask "what on god's green Earth would lead me to thinking Voyager would be good" ... but TNG was good, and DS9 was gooder. Therefore it would be a fair assumption that Voyager was around the same level of goodness as those, and it had a great premise.
Why would I assume it's going to be bad until I actually saw it?
Voyager isn't really all that bad, it just has a few really lame episodes that are on par with Season 3 of TOS. But I'm only on season 2 right now, and I'm expecting that things will pick up in later seasons (notable new cast member yet to appear).
Remember, TNG season 1 had Super-Wesley saving the day almost every time anything needed saving (they stopped doing that due to fan backlash), the female doctor was fired for season 2, but brought back because the new doctor wasn't really clicking with the cast, and season 1 seemed to go through a new Chief Engineer virtually every episode that had engineering in it. I'm still not sure what was up with that: casting troubles? A desire to minimize the focus on engineering in favor of the bridge crew? IDK. DS9 didn't have the casting issues of TNG but they took a couple of seasons to work out the true focus of the show.
BTW, every Star Trek series had it's terrible episodes. The Pherengi Sex Change episode from DS9 stands out here.