I dunno. The Borg should have been the primary antagonist. Ideally, the Borg "arc" (term used loosely) would've been VOY's Dominion War. In theory, VOY could have been even better than DS9.
But just a general low quality kept that from ever happening.
In my mind, there's a nebulous concept of a perfect Voyager that plays out a lot like Star Trek: Battlestar Galactica, except the Cylons are the Borg, and Tom Zarek is Chakotay. It's weird to think, given the wholly different atmosphere, themes and competence level, how similar in the basic story both shows were. (Except with one you didn't know it was bad until the last forty-five minutes of the series. So, hey, I guess Voyager wins points for straightforwardness and honesty.)
People keep saying this, but I just don't see it. Most of the stuff in BSG just wouldn't have worked for VOY, at all.
As for the VOY Aliens, the only ones that really stunk were the Kazon. The others would've worked out better if they'd been kept around, but the backlash from the fans kept that from happening (that and Jeri Taylor). They just didn't WANT any new Aliens to begin with.