I agree with what you're saying about the in-universe sketches not being riotously funny, but that doesn't bother me, because they're not really a part of the show. The most we ever see of one is about thirty seconds.
A point of contention there is that almost every time we see a part of a sketch, it's in or followed with the context that Matt (genius writer character) doesn't like it and it needs work.
As such, I don't think it's a failing of the premise.
I agree that the pilot is very strong, and in the back half of the 22 episode run, things tend to play to Sorkin's strong points (IE, a five episode story arc about one of the cast members' brother being missing in a war zone) but by that point, I'm so involved in the huge, likable cast that I don't care.
Furthermore, I agree that the essential problem with the series is that Sorkin tends to take shit very seriously, and fill a situation with smart people - and that in comedy, it's more difficult to buy than in politics. (Insert joke here.) This trajectory even seems to continue; the last thing he wrote was The Facebook Movie, which I read and enjoyed, but felt that problem's presence in.
However, as seriously as it takes its characters, I think it's a deeply enjoyable show, with a much higher frequency of brilliance than almost any other program since The West Wing's first four seasons.
In other words, I mostly agree with Mike, however I can't recommend the show enough.
And, not as a competitor to Studio 60 but as its own show, I still can't believe anybody can watch 30 Rock.
I have a tendency to fix your typos.