Too often I've heard this defense of a lesser movie: "Well, now that they've set everything up they can get to the good stuff in the sequel!" I've heard this touted around in relation to Green Lantern, and this sentiment really started to permeate the public consciousness around the first X-Men (and, to a lesser extent, the first Spiderman).
Although this is common in many genres, superhero movies suffer strongly from this affliction. The first movie gets the origin out of the way which should lay the groundwork for the "real" meat & potatoes we've been waiting for, but in actuality the second movie more often than not attempts to replicate the same formula as the first but BIGGER.
On occasion it's done better. Spiderman 2 is a strong example, in which much of the same story is regurgitated (Peter gets no respect at school or at his job, he yearns for Mary Jane, butts heads with his friend Harry, has a father figure that is ironically turned into a super villain he has to fight, and even gets to be normal again in order to regain his powers) but is improved upon.
Some might argue the same of Terminator 2. A second movie can go a long way towards deconstructing the character and plot beats of the first. With success, there is not only improvement but new light shone on the first.
Along those same lines, a sub-genre can be long established before the "best" of its kind comes along. I'm sure there were movies featuring a lone average Joe facing impossible odds before Die Hard, but you'd be hard pressed to argue against it having perfected the formula. Halloween, meanwhile, follows many of the same beats as Psycho and the Texas Chainsaw Massacre and synthesizes them together as a whole new beast.
Can a movie be faulted for using the same formula as another movie if it improves upon and even perfects the formula? With that in mind, what are the best (and worst) examples of movies that have perfected an already established cinematic formula?