In 'Christmas with the Joker', the Joker was portrayed as a humorous, slapstick comedian who was also a crazed, vicious killer who wanted to murder people in horrible ways, and being just plain evil and merciless. This episode chooses to look away from that evil side that defines the Joker as Batman's archnemesis, and focus more on the comedy.
The Joker in this is pretty ridiculous, with very camp, Adam Westish one-liners, and he says so many unfunny jokes that it just gets tiresome. His plot is not as twisted and insane as with all the other times. He just wants people to go mad so he can easily rob them. That's what any ordinary crook would do if they got their hands on some laughing gas. And the Joker is not meant to be an ordinary crook.
Although this episode is mainly an unsuccessful comedy, there are traces of darker elements. It is said that the gas could result in permanent insanity, and Alfred looks pretty insane when he's suffering from the effects of the laughing gas, and this adds a personal note to Batman's mission against the Joker. The Joker also clearly intends to murder Batman, but this is spoiled by the childish clown music and wisecracks that accompany him.
The music score is actually very good, but not really suited to this episode. The animation is, as usual, superb, but this episode suffers from the poor script and disrespectable portrayel of the Joker. There may be some good action sequences, but this is definately not Batman at its peak. 1.5/5.