Any sketch comedy is going to be hit or miss. RC usually bats it out of the park on their Trek and SW parodies though. This one is pure genius...
http://www.youtube.com/watch?v=iauuuhpSfRQ
I've never seen them parody any of the later series except for TNG.
I feel Patrick Stewart is too good an actor to be slumming it in Seth McFarlane's shows, but then again he was in LifeForce. ;)