Star Trek

I realize some didn't like Neelix, but he was essential to their survival.  On one of their first stops to collect edible fruits and vegetables, Carey showed Chakotay an apple-like fruit that Neelix said, "One bite will kill ya!"  They could have all died.  Neelix had his good moments too.  I liked B'Elanna, but I think they could have brought her down an octave or two as time progressed, but she kept that short fuse all through the series.

I disliked Threshold the most.  Total waste of film.  They could have taken that in a whole different direction.

Least favorite character was Tuvix, least favorite episode was Threshold.  Fortunately, that episode was retconned, and is now considered to have been a dream that Paris had.

All the characters are great in their own right, but my least favorite, if I'm honest, is Seven. Jeri Ryan is a great actress but the whole dynamic of the show changed after her arrival and I don't think always for the better. If they had left J/C alone, then I could be more forgiving, but Seven came to trespass on everything I loved about the show.

Least favorite episode - harder to choose as I love almost all of them, but I would have to say Endgame for the sheer disappointment of C/7. Spiritfolk, Human Error and Threshold are also amongst those I liked least.

As to least exploited storyline, I'd have to say the Maquis. They and Starfleet worked together a little too easily, imo. Overexploited storyline for me was The Borg.