Majel Barrett Roddenberry in the role of Nurse Chapel. She's a two-dimensional damsel in distress.
Marina Sirtis has all but admitted she is a soap-opera actress. Between "The Child" and "The Loss," she proved that to be true. I can't stand Gates McFadden's huffing and puffing as she asks the Captain, one more time, to break the prime directive and treat a patient. And of course, there's Wil Wheaton. No more needs to be said.
As someone else said, I wanted to like Avery Brooks' performance. He had some moments that he shined and he was much better towards the end of the run of the show. But in seasons 3-5, he was a set-up for a commercial break. Dramatic line, punch up the music, fade to commercial. It really plays badly in today's binges on Netflix. I'm surprised no one has mentioned Alexander Sidding. He looks disinterested most of the time. They would give him a dramatic line, and it's like he'd make fun of it. He's the one who couldn't carry the Section 31 episodes, everyone else was great.
People talk about Terry Farrell. I think she brought a confidence to the character that would come from total acceptance of yourself after having the knowledge of 7 lifetimes. I thought she was playful, not a comedian. She just had a sense of humor and smiled a lot. I like her performance in "Rejoined." The direction needed some work, especially the setup to the last scene. But her performance was fine.
Voyager. I like Kes, I like The Doctor. Everyone else couldn't act their way out of a wet paper bag.
Nothing was really wrong with the performances on Enterprise. They had a solid cast, just didn't do a whole lot with them.