First off, Yuen Biao is amazing, and teaming him with Sammo Hung always makes for a good movie. Fans of those two should definitely see this one. The problem here is that this film doesn't get to the good stuff until 2/3 of the way through.
The first third is mainly over-the-top goofy comedy where Yuen Biao and his brother try to work various scams on unsuspecting people. I usually like Sammo's comedies, but this part seemed to fall flat. I think that's because it tried too hard to be goofy and funny, for example the characters are constantly twitching and making silly faces.
The second third is a mix of comedy and kung fu when the brothers undertake some training. This part comes off fairly well and nicely sets up the story for a twist that takes off in the final third.
The final third of the film switches to a typical training-for-revenge story, and this part is downright great. Yuen Biao undergoes some of the best training scenes I can remember and finally gets to let loose and show his stuff. This culminates in a long fight scene with the villain that's both intense and inventive. If the whole movie was like this I'd give it a nine or ten, but it's weighed down by the first parts to end up just above average.