Mamet is not an unalloyed mastermind in my book. He hits and misses.
Here, he (and Shel Silverstein) crafted a story that explores a few clever plot concepts, such as the vaguely "Inspector General"-style false-identity gimmick. No spoiler, there: It kicks in pretty early on and dominates things for most of the flick. Most of the comedy/tension of the flick revolves about that idea.
The truly touching stuff involves the ensemble work, and it's worth taking the flick in of an evening just for that.
Other than that, the structure/storyline of the flick is about 80% good, but about 20% sprinkled with confusing side-events that don't quite seem to mesh.
Mamet and Silverstein tried to engineer a truly compelling denouement, but it doesn't feel quite whole and organic and... compelling, to me. It's merely adequate, in my book.
But if you want to see truly inspired acting, driven by adequate direction, check it out.