The Man Show may have had its issues, but it was enjoyable to its target audience. I imagine watching it today would be kinda cringe-worthy, but so are many other things.
What I do think is that it really was sort of the proof in concept for that type of show (talk show/skits/etc) being able to work and attract viewers. Without it, I don't think we get Chappelle's Show and Crank Yankers, which also led to things like (unfortunately) Mind of Mencia and (fortunately) Key and Peele and Drunk History.