Once Seven came on, Voyager became so much more science/tech oriented because her character brought that option. They were able to do so much just because of her having so much more technological experience as a Borg. After assimilating 8,000 + species I'm a bit surprised that they weren't able to do even more than what they did do.
I know there are a lot of Seven haters out there, and I understand why given that she was seen as a sex object, which ironically is the absolutely not what her character represented. Seven didn't even begin to get into a romantic range of emotions until the last year of the show. Janeway was the only female character that could come close to competing with her as far as having few to no romantic entanglements, but even she had more than Seven.
Seven was really a great character that brought a lot to the show, but I think some Trek fans didn't like that once she came on she was a key character and also that the character development of some of the other cast and their personal storylines diminished. I like that we didn't have to spend a lot of time on that. Kes and Neelix were the only species aside from Seven that we weren't familiar with and we got plenty of episodes where they were important or had major storylines. I guess it's just my own thing that I would much rather have a good scifi episode than an alien character episode. There's only so many of them I could take. Most of the ones Voyager had were well done and gave the show enough balance between Voyager situations vs. character situations.