Mark Osborne and John Stevenson's computer animated comedy Kung Fu Panda does exactly what it says on the tin, spinning a familiar story of triumph against the odds around a rotund bear with a passion for martial arts. Jack Black is perfectly cast as the voice of the eponymous guzzler, who sees himself as "a legendary warrior whose fighting skills were the stuff of legend".

"He was so deadly, his enemies would go blind from his awesomeness!" adds the bear in a hilarious opening monologue, complete with two-dimensional animation, to tip us off that the portly protagonist has a febrile imagination to match his considerable girth.

Big is beautiful in the best family-oriented offering from DreamWorks Animation since box office smash Shrek. Colourful visuals and excellent vocal performances, including Dustin Hoffman as an acerbic mentor, guarantee a lively 92 minutes of low blows and last-gasp victories, disproving one naysayer who sneers "that flabby panda cannot possibly be the answer to our problems".

He's definitely the answer for parents who need to keep pint-sized charges amused this weekend. Po (voiced by Black) has a passion for kung fu, though no natural ability. Instead, he is destined to inherit the family shop run by his long-suffering father, Mr Ping (James Wong).

Unthinkably, local sensei Master Oogway (Randall Duk Kim) anoints Po as the next Dragon Warrior, who must protect the village from the threat of escaped prisoner Tai Lung (Ian McShane). Oogway's choice of successor stuns his protege Shifu (Hoffman) and loyal students Crane (David Cross), Mantis (Seth Rogen), Monkey (Jackie Chan), Tigress (Angelina Jolie) and Viper (Lucy Liu), better known as The Furious Five.

These fighting masters feel certain that Oogway should have chosen one of them instead and wait patiently for Po to fall by the wayside. The bear meanwhile is delighted to be in the presence of greatness. "Whoa! The Furious Five!" he gasps. "You're so much bigger than your action figures... except for you Mantis, you're about the same size!"

Under the tutelage of a despairing Shifu, Po aims to meet his potential, presuming he can keep his mitts off the temple's stash of cookies.

Kung Fu Panda wins us over instantly with its lovable characters and affection for martial arts cliches as the overweight hero discovers his inner strength somewhere within that growling belly. With lots of heart and a profusion of broad humour, Osborne and Stevenson's film gently promotes Mr Ping's mantra that "to make something special, you just have to believe something is special".

Fight sequences are animated at breakneck speed, matched by quick-fire banter between Black's ill-equipped saviour and Hoffman's dour master, whose entire reputation rests on a dreamer who runs out of breath half way up the temple steps. Thankfully, the film keeps up a head of steam(ed dumplings) until the rousing final frame.

With great power comes great responsibility . . . not that bona fide superhero Hancock (Will Smith) cares. The eponymous protagonist of Peter Berg's all-action adventure is another victim of our celebrity-obsessed times, seeking absolution in a whisky bottle to cope with the pressures of fame. Unfortunately, this self-loathing crime fighter has no time for rehab - all he wants is a park bench to rest his weary head, from where he can spout obscenities at passing women and children. For the opening hour, Hancock delivers everything you expect from a Will Smith blockbuster, including spectacular set pieces and wisecracks, albeit with an excess of strong language and crude humour, which should concern parents of younger children. The pièce de résistance is the superhero serving time in prison and exerting his dominance over two thuggish inmates by threatening to shove one man's head where the other's sun don't shine.

Eye-watering facial expressions and nifty special effects prove Hancock is true to his word. This time behind bars sows the seeds of the character's redemption and then without warning, Berg's film abruptly morphs into something else entirely.

Laughter abates and the mood turns increasingly serious as scriptwriters Vy Vincent Ngo and Vince Gilligan throw us a succession of narrative curveballs, hastily introducing a pivotal character to explain Hancock's back story and propel the film to its sombre resolution. As the one and only saviour of Los Angeles, Hancock begrudgingly rescues beached whales, thwarts bank robbers and helps to maintain peace on the city streets, except his headline-grabbing exploits always result in millions of dollars of damage.

Drunk, foul-mouthed and deaf to an ever-growing chorus of public dissatisfaction, Hancock rescues publicist Ray Embrey (Jason Bateman) from a collision on a level crossing.

As a thank you for saving his life, Ray vows to restore faith in the misunderstood superhero.

However, the so-called "Bono of PR" faces an uphill battle to curb his client's excesses, ignoring his dutiful wife Mary (Charlize Theron) who warns, "You see the good in everybody, Ray, even when it's not there".

With the credit crunch biting hard, Hancock potentially offers great value for money: two screenplays - one a comedy, the other a doomed romance - welded together for the price of one ticket.

Evidently, writers Ngo and Gilligan hope to please everybody, some of the time.

Despite the haphazard plotting, the second half is much more interesting but hinges on a twist that can't be revealed or discussed here.

Smith's natural likeability smoothes some of his character's rough edges but he delivers his best work when Berg's film cuts the comical asides and forces the superhero to take a long, hard look at himself in the mirror.

Bateman and Theron are underused and director Berg orchestrates the action sequences with aplomb, ultimately letting the digital trickery run rampant.