chicagoist.com has posted a spreadsheet indicating which RW deals are particularly good and bad; there's an introductory article (click
here), or you can go straight to the spreadsheet (click
here). They also posted another article, "10 Tips To Avoid Losing Money During Restaurant Week" (click
here).
Their entire analysis is based on the pricing of the RW menu as compared with paying for the same menu items on an a la carte basis. That's one way to analyze the value of the RW menu, but not the only way. For example, some of us were considering going to L. Woods in Lincolnwood for lunch during Restaurant Week. The $22 RW lunch menu represents a decent value when compared with the same three courses (soup/salad, entree, dessert) purchased separately, but that represents a HUGE amount of food, and most folks going to lunch there would likely spend less than $22 and only order one or two courses rather than three. So the RW menu might or might not be a good value, depending on how you look at it.
As a general rule, I think Restaurant Week works well when you find a RW menu with dishes that sound appealing to you, and which would otherwise cost more or not be available.