Although I don't watch Voyager as much as the other series (it's the only series in which if I were asked to describe an episode just from the title, I'd find it a struggle Season Four onwards). I actually enjoy the earlier seasons more, and while I've nothing against 7 of 9, I think the Borg were overused towards the end.
I don't think they really jumped the shark, so much as failured to live up to its premise, yes the crew spent seven years looking for a way home, but the conflict between Starfleet and Marque crew members forced to work together just wasn't built on the way character conflict on DS9 was. And there was no sense of the crew getting more desperate as time went on (unlike Season Three of Enterprise) so no matter how many shuttles were destroyed or torpedoes fired, the ship never seemed depleted of resources. The show should have been more like 'Year of Hell' all the way through.
"Commanding a starship is your first, best destiny."