Mrs Brown's Boys is incredibly successful, I think its appeal is in its uproariousness, unlike the middle class twaddle that Robert Lindsay appears in (which is also popular). Naturally, a man playing a woman is a handy panto gimmick.
I have to say that Mrs Brown's Boys seems to be a succession of stand up one-liners masquerading as a script, but I'm always being accused of "dissecting" stuff instead of just enjoying it.