Personally I like Threshold. Yes I can see why people don't like it and theres aspects in it in which I cringe, but overall it definitely has enough humour in it to make me like it.
I was sad when Kes left but I agree with her need to go, she wasn't a particularly interesting character and didn't hold that much fascination and importance in the series. So when Seven came to the show I instantly liked her, she brought a spark to the show and sped up its course and gave way to new and exciting plots with the borg encounters and such.
However I am finding that though important to introduce her to the show by incorporating her into a lot of the episodes heavily, it seems as though they have seemed to forget about the rest of the cast as they seem to be included more in the background of the episodes. But I'm only half way through season 5, I guess that may change as I watch more. But either way Seven has made a fantastic addition to the show.
But when watching earlier seasons of Voyager with Kes in it, I instantly feel a sense of longing for her back because I miss her. So I do love both characters.