This week's '30 Rock' seemed to be tightly reigned in, and devoid of most of the traditional shenaniganry (and we're not exactly sure that's a word, but it certainly applies to '30 Rock'). Jenna's antic's were toned down, Tracy was well-behaved, and I think the only "wacky" moment in the whole show came from a boxing dummy.
This isn't to say that the show wasn't funny - it's just after nearly a whole season of craziness, a "bottle episode" (no guest stars, limited sets and effects, etc.) comes as a bit of a surprise.
In this case, show's standard three mini-plot formula proved useful, keeping the focus from staying too long in one place helped to keep things from getting dull.