The acting from Jurasik and Katsulis was great. Furlann, too, considering her role was sorta Space Galadriel + Space Mom. My friends and I used to joke the actors on the show couldn't play convincing humans, but the people playing aliens were terrific.
(I guess Jerry Doyle playing Jerry Doyle was perfect as Garibaldi, since Garibaldi was just Jerry Doyle)
Heh. Bill Mumy FTW!
I will give credit to Michael O'Hare, who was excellent in an otherwise ... uneven .... first season.
And to Bruce Boxleitner, who was an excellent Sheridan.
But yes, a lot of the actors that were cult favorites on the human side, from Claudia Christian, to Jeff Conaway (RIP), were just not very good. Richard Biggs was ... serviceable in an underused role, and some (Patricia Tallman, Andrea Thompson, Jason Carter) were, um, oof.
I loved, absolutely loved, Walter Koenig playing against type though. Watching him chew the scenery is one of the great pleasures of the show.