TNG, DS9 and Voyager all rotated the main character for each episode. This worked best for DS9 where all the main cast were different but interesting. It easily had the best supporting cast. Every Garak episode was great.
Denise Crosby left TNG on the basis of "my character is dull I want out". That was the correct decision although her guess appearances later were great. By contrast Troi's mother and Worf's son were both dull.
Voyager had the blandest characters. It also had the blandest aliens (apart from the Borg). In many episodes it was battle scarred but in the next episode it was as good as new. Also if it was racing across space then why did it ever encounter the same aliens twice.
Enterprise had several bland characters and episodes although Shran was great.
Never liked the serialised approach of Discovery and Picard.
Really hoping "Strange New World" will get things back to normal. Pike, Spock, Number 1, Uhuru, Nurse Chapel and others and also episodic.