There are a few select great films released each year, a fair amount of good and bad ones, and an overload of mediocrity. The truly awful ones may be the most difficult to sit through, but even more disheartening than them are the motion pictures that start well and with a whole lot of promise, then proceed to fall apart as they fail to live up to their obvious potential. "Cowboys & Aliens" fits this egregious latter model to a T, surpassing even hopeful expectations at the onset with an imaginative genre-mashing setup and a focus on characters before fireworks, then collapsing with a blunt suddenness midway through as hokey revelations and an overload of wheel-spinning take over. It's amazing how quickly it happens, proving all the more how a couple misbegotten ideas can derail an entire film's initial trajectory. Probably not helping matters are the five—count 'em, five—writers credited to the screenplay, Roberto Orci & Alex Kurtzman (2009's "Transformers: Revenge of the Fallen"), Mark Fergus & Hawk Ostby (2006's "Children of Men"), and Damon Lindelof (TV's "Lost"). Too many cooks in the kitchen will ruin the finished outcome practically every time, and not even director Jon Favreau, coming off of 2008's "Iron Man" and 2010's "Iron Man 2," can wrangle in the mess that's made.

In 1873's Wild West, Jake Lonergan (Daniel Craig) awakes with no memory of who he is or how he got there. He holds a photograph of a woman (Abigail Spencer) he thinks he ought to know, and around his wrist is a strange, bulky iron shackle. Making his way to the nearby town of Absolution, Jake and his mysterious stomach wound are tended to by kindly preacher Meacham (Clancy Brown) before wasting no time in standing up to and crossing big-headed jackass Percy (Paul Dano), son of gruff town-runner Colonel Woodrow Dolarhyde (Harrison Ford). Elusive stranger Ella Swenson (Olivia Wilde) senses a connection with Jake and seeks him out, unwilling to reveal what she already knows about him. Then lights in the nighttime sky appear, and before long the townspeople are being snatched right off the ground and into flying aircrafts. Talk of demons and monsters break out as Jake, Ella, Dolarhyde, Dolarhyde's right-hand man Nat (Adam Beach), suddenly orphaned pre-teen Emmett Taggart (Noah Ringer), and saloon owner Doc (Sam Rockwell) take to their horses in pursuit of the creature tracking footprints across the Arizona desert. Where they find the otherworldly culprit is where they hope to free their abducted loved ones.

Loosely based on the 2006 Platinum Studios graphic novel created by Scott Mitchell Rosenberg, "Cowboys & Aliens" has a crackerjack premise at its core. Combining a classic western with a sci-fi alien invasion is something that has never been done before on this large of a scale, and it opens the floodgates to explore any number of topics involving people from a bygone era who are faced with something from outer space that they know nothing about. In the 19th century, very little had been discovered about what was beyond the earth's sky and the very concept of aliens would have been totally foreign to them (hence why the characters suggest they might be demons after the first attack). It's a remarkable, thought-provoking notion, really, and one that director Jon Favreau could have delved deeper into than he ultimately does.

The first hour, at least, offers up all kinds of hope, the story nothing less than absorbing as it takes its time to develop the earthbound mysteries and conflicts and introduce all the major players involved. By the time the aliens arrive, the viewer has become so entrenched in the movie's world that the sci-fi element has been all but forgotten about. The town assault that follows is blunt and brutal, building the terrifying awe of such a situation while unavoidably calling to mind a similar set-piece at first act's end in 2005's "War of the Worlds." The quest that follows amidst the sand and rock formations of the picturesque desert locale isn't far removed from 1956's John Ford classic "The Searchers" or 2003's Ron Howard western drama "The Missing." The first direct interaction with an alien creature—involving young Emmett as the men take shelter in a capsized boat they find—holds a level of queasy terror that the otherwise terrific recent "Super 8" lacked, and a later sequence where the group are once again accosted by the UFOs and Jake hops on the back of one to save Ella is genuinely thrilling. The first-rate visual effects work aids in making the audience believe what they're seeing; it's all pretty seamless.

Like a spell instantaneously broken by a witch's nose wiggle, the film's good will dissipates the very second the cockamamie, nonsensical resurrection of a character comes into play, followed immediately after by an explanation of the villains' motives so astoundingly dopey it's got to be seen to be believed. Was this the moment where one set of writers took over for another? No matter, the picture goes downhill from here, the tension and intrigue decreasing like air from a balloon. The characters, too, get lost in the chaotic, empty-headed action that follows, culminating in a climax that has no business being the frivolous, indifferent bore that it is. By the end, it is simply frustrating to consider how far the proceedings have fallen over the course of the last sixty minutes.

Performances very much keep with the appropriate theatrics of the western genre. Daniel Craig (2008's "Quantum of Solace") is commanding and stoic as Jake Lonergan, a strong, silent type whom one wishes would emote a little to show that he actually feels anything. As Dolarhyde, Harrison Ford (2010's "Morning Glory") alternates between soft but intense threats and outright growls; the older Ford gets, the more he appears to be turning into a grizzly bear. Olivia Wilde (2010's "Tron: Legacy") is either just okay or quite good considering she is faced with the confused, virtually unportrayable role of Ella. She doesn't do much with it, but no one else could have, either. The rest of the ensemble is filled with established talents who deserve more to do—i.e., Sam Rockwell (2010's "Conviction"), Adam Beach (2006's "Flags of Our Fathers"), Paul Dano (2011's "Meek's Cutoff")—and a child actor, Noah Ringer, who is infinitely better here than he was as the wooden lead in 2010's fantasy fiasco "The Last Airbender."

"Cowboys & Aliens" is moodily and attractively photographed by Matthew Libatique (2010's "Black Swan"), the widescreen vistas popping on occasion and the special effects integrated into the dusty, sun-dappled images with aplomb. Art direction and production design are never in doubt, while the music score by Harry Gregson-Williams (2010's "Unstoppable") wavers between inspired and forgettably conventional. Tech specs only go so far, and that's where the problems befall this effort. As meticulous and deliberate as the narrative is early on, it is just as clumsy and ineffectual in the second half, momentum and thematic substance tossed to the wind in exchange for ill-considered developments and actions that feel like they've been devised on the spot. "Cowboys & Aliens" is bereft of a singular vision, and no wonder; with a half-dozen people responsible for the story and screenplay, it's a wonder even the first hour stayed on track as long as it did. If only movies could have re-dos in lieu of remakes, then perhaps this one might have been able to live up to its clever title.