The last Vidiian episode closes the Phage-ridden species on a hopeful note, and if that's not enough to celebrate, then how about a pretty significant development for The Doctor?
The Vidiians were alien menaces who preyed on our crew for body parts and potential cures, and they were always fun, always providing series highlights, but they were also fairly one-dimensional, perhaps understandably so, because according to their timeline, they'd been suffering the Phage plague for an incredibly long time. "Lifesigns" is an indication that they aren't all that bad, so chances are they used to be pretty good, actually. We meet a Vidiian who longs to be seen for something other than her disease, and thanks to the Holodeck, we actually do see what a Vidiian would look like without all the degeneration.
The Doctor, meanwhile, gains her as a love interest, and it forces him to be something other than acerbic for the first time, and it's a huge breakthrough. It's because she sees him for something other than a program, much as he sees her for something other than her scarred appearance. Sure, Kes has always been supportive, but there was always a distance, like a quasi-academic relationship exists between them. Kes is a project for Tuvok, and The Doctor is a project for Kes. (There's a lot to say about Kes, but this is not really an appropriate moment.)
Later, of course, the Vidiians are revealed to have been cured by the Think Tank, so it's anyone guess where their story goes from there, or what might have been possible if Voyager had been able to stick around any one region of space for more than a few seasons. The fact that the writers seemed to push it with some regions gave us a lot more than some fans sometimes appreciate. This is definitely one of those moments.
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Memory Alpha summary.