Harry Kim was so boring that they even made it part of his character lore pretty much.
Coming off of DS9, which probably had the strongest secondary characters of any Trek show (Quark, Garak, Odo...I mean fuck, even the villains like Dukat and Weyoun), Voyager was so bland from a cast perspective.
Tuvok: I mean, he's a Vulcan. Enough said.
Chikote: Zzzzz
Harry: Zzzz
Tom: "Time for 20th century references!"
Neelix: Welcome to Holiday Inn. We serve breakfast at 8am
B'lana: Me angry half-klingon with mommy issues
Janeway: I'm like Picard, but with less Shakespeare and somehow more dull
The Doctor: Literally the best character on the show
7 of 9: Literally the best pair of supporting characters on the show
The biggest issue was you never really felt that most of the characters really grew. Besides the season 1 Marquis shit that was quickly resolved, you never really felt like most of the characters had progressed very much beyond Doctor (who was becoming more and more of a real person) and 7 of 9 (who had the whole rediscovering her humanity arc). I mean, maybe B'lana in the sense she became a more accomplished engineer and her whole relationship development with Tom. But beyond that, you didn't really see the same progression like you saw with characters like Worf or Odo or Quark or Data or Geordi.