Some of the characters were pretty weak, added to that poor writing and all the fanwank over Seven and you get a bad situation for the series.
Janeway started off a good character, both Captain and scientist. But as the series progressed there was little consistency, swinging from upholding UFP law to the letter to attempted murder of Noah Lessing. Had they picked a direction and stuck with it (either as someone who will hold onto the rules and regs or someone willing to do whatever needed to be done to get home). She needed more to her, other than simply being billed as Star Trek's first female lead.
Chakotay was very dull. Aside from being a Native American Maquis there didn't seem to be much else to him. He should have been angrier and more abrasive, butted heads with Janeway at every opportunity, make him more focused on his people than the crew as a whole. This would change over time, as would his relationship with the Captain, both becoming far more complex.
Tuvok I loved. A proper Vulcan who showed us the logical use of violence. But of course he suffered from the Seven Syndrome, once she arrived he fell into the background as was his friendship with Janeway.
Tom Paris I have always been kinda 'meh' about. A decent enough character, a few interesting stories, though didn't understand the relationship with Torres, though it was well done. All in all pretty inoffensive.
Torres is another character I loved to fell victim to Seven Syndrome. All the things she would have done went to Seven in later seasons, leaving her with just the Paris relationship to develop. One thing they did with her that I hated was having her accept her Klingon side, she was far more interesting when she hated a big part of who she was.
Kim was dull from his first to last scene. The idea of a green ensign is interesting, but after a year lost in the unknown he'd have grown some balls and would begin to mature, instead he whines about wanting him mummy for years. He should have died in Scorpion (serious, who'd they poll to find him attractive?).
The Doctor was alright but over time he really started to annoy me. They did far too much with him, made him too great and wonderful at everything, even got him in command of the ship. They should've left him stuck in Sickbay.
Neelix. Where to start? A hated character, whose role as cook could have been held by some extra, as a guide he became useless, he never did anything as morale officer, and as ship's ambassador he was a joke. The character should have been more rugged and darker, more of a Han Solo scoundrel.
Kes came into her own after she finished being Neelix's girlfriend (to this day that is still creepy). She had potential and lots of directions open to her, but they got rid of her needlessly.
For me, Seven ruined VOY. If she wasn't the cause of storylines she was the cure for them. The idea of a former Borg recovering their humanity was interesting but poorly done. For one, her implants should have been removed over at least half the season, becoming less of a drone with each episode, but since she was just there as a sex symbol then they couldn't have that now could they.