Movie trailers are spectacular. Short and punchy, they are meant to give the viewer an idea of the film and display some of its finest moments: terrific explosions, hearty laughs or a beautiful romance. A well-made trailer can make any movie, regardless of its premise or star power, seem like the next big hit. The trouble with trailers, however, is that sometimes they give away too much of the movie.

Usually, trailer excess is a problem of humor — how many times has a comedy’s trailer used up all its good jokes? It’s really no fun to see a movie and find you’ve already laughed at the funniest parts. Other times, however, trailers can give away too much of other aspects of a movie: character development, for instance, or narrative.

Such was my worry with “Hancock,” the most recent in this summer’s long line of superhero movies. “Hancock” stars Will Smith as a superhero with a bad attitude, who works with idealistic PR man Ray Embrey (Jason Bateman) to revamp his image. I was hesitant about “Hancock” because this was all readily apparent from the preview. It seemed to me the trailer showed Hancock’s entire metamorphosis, from messy drunk to clean-shaven hunk (yes, I meant for that to rhyme).

Fortunately, for me and for “Hancock,” there’s more. I won’t get into details about what happens after the image change, but I will say it involves Hancock’s past, and a mysterious superwoman. It’s almost as if “Hancock” were two movies rolled into one, the first about a super-strong bad boy gone good, and the second about a lonely demi-god searching for his place in the world. This split in the film’s narrative leads to a lot of lost nuance and undeveloped sub-plot; there is an eagle motif that runs throughout the movie but is never explained, and a fair amount of mythology surrounding the second half of the storyline that just doesn’t make a whole lot of sense. Screenwriters Vincent Ngo and Vince Gilligan have essentially crafted two rather compelling scripts, but seemed to haphazardly put them next to each other rather than integrate them as well as they could have.

That being said, “Hancock” is in all other ways a terrific film. Will Smith plays the sneering, whiskey-guzzling superhero as effortlessly as he always does, combining hilarious and foulmouthed off-the-cuff comebacks with a more than convincing depth of emotion. Say what you will about Will Smith, but the guy can act. Jason Bateman is as hilarious as always, though he can’t quite pull off the innocent idealism that his character requires, and the hand of director Peter Berg is smooth and steady.

What surprised me the most about “Hancock” was how funny it is. The laughs come fast and loud in the first 20 minutes, setting the tone of the movie the way a first act should. Even when several of the jokes are recycled later on — let’s just say I’ve heard more than enough about sticking one guy’s head up another guy’s ass, thank you very much — the movie has enough momentum that they don’t fall flat. The transition between the comedic focus of the film’s early parts and the more dramatic second half is smooth as well, though that transition is overshadowed by the glaring lack of transition in the plot.

Ultimately, “Hancock” is definitely a movie worth seeing. In a summer schedule filled to overflowing with superhero movies, “Hancock” brings an exciting sense of originality and freshness to the table. Unlike “Iron Man” or “The Incredible Hulk,” “Hancock” does not rely on a comic book mythology that has to be explained to anyone who isn’t a Marvel nerd, and its edgy sneer might be just the satirical jolt the superhero-movie genre needs. “Hancock” may be two movies rolled into one, but it’s two really fun movies.