I found myself getting hooked on this new show quite quickly - the writing is smart and the dialog is witty and fast-paced. It's the sort of show that requires your full attention, and rewards your effort with lots of quick smiles, jolts of surprise and excitement, and a feeling that you've just ridden a really fun amusement ride.
The sad thing is that the show seems to not be doing well with viewers and may be cancelled due to low ratings. The show is by no means perfect: The major weakness being that the show's comedy routines and comedy stars are not that funny. That's a bit of a problem when the show is meant to be about a comedy show. Ken Levine's blog has an interesting comment on the show, and a link to a YouTube parody/comment on the show.
(Psst! Ken's blog is well worth subscribing to)
I'll keep my fingers crossed and hope that Aaron Sorkin won't go too far into the Romantic Comedy swampland in an attempt to lure viewers.