If it ain't broke -- don't fix it.

For anyone who has seen "The Hangover" and loved it, it won't come as any big surprise to see that adage at work in "The Hangover Part II."

Todd Phillips' sequel to the most successful R-rated comedy of all time is just as raunchy and just as preposterous as the first movie's trip to Vegas. He takes the formula and re-heats it.

The film's colourful heroes also awake in another strange city, this time in Bangkok, with no clue how they got there.

But repeating history, rather the reinventing it, is where director Phillips makes his fatal mistake with this sequel.

As the film begins, Ed Helms' character, Stu, is about to walk down the aisle on a beach in Thailand.

His fiancée's father loathes him.

His fiancée's brilliant teen brother makes Stu look like a total loser to the bride's family

Stu withstands these pressures thanks the support of friends like Phil, played by Bradley Cooper and Alan, played by Zack Galifianakis. They've all travelled to Thailand to stand by their pal.

But Stu is no fool.

He knows that trouble follows this "wolf pack" wherever they go.

To avoid a repeat of Vegas, Stu insists that no bachelor party takes place in his honour. He organizes and reorganizes every wedding detail so that nothing goes wrong.

Despite all his efforts, an innocent toast to the groom on the beach lands Stu and his buddies in some seedy Bangkok hotel.

No one knows how they got there.

No one knows why there's blood on the floor or why a detached finger is in the room.

More important still, these grimy, sozzled American tourists can't figure out where Stu's future brother-in-law is. The 16-year-old whiz kid is missing in action.

All these boys know is that a chain-smoking capuchin monkey is in their room and that Stu's wedding is a day away.

With time ticking down, the friends pool what wits they have left to solve this mystery and get Stu married as planned.

Bangkok isn't so merry for "Hangover 2's" heroes

"Hangover 2" does have some good things going for it.

Phillips definitely pays more attention to character development in this entry.

That's particularly the case with Helms' character, who goes from a nice, well-meaning doormat to a guy who can stand up to his condescending future father-in-law.

The dynamic between the alpha male Cooper and Galifianakas' nutty man-child Alan also gets fleshed out nicely.

But for all its gross-out fun, "The Hangover Part II" feels like more of the same.

There's no real rush of excitement. No breathless laughs come after these pals find their sanity and find their way home.

What made "The Hangover" so great was that it was shocking. It was unlike any other buddy road trip Hollywood had seen.

It also captured the pulse of entire generation.

Greatness like that is nowhere to be found in "The Hangover Part II."

When Phil and the gang finally regain consciousness and return to the land of the living their raunchy ride does inspire some good laughs. But the overwhelming feeling they leave us with is that we've all travelled down this drunken road before.

Two stars out of four.