I read one of their first plays, The Sorcerer, a few days ago. I'm going to give a bit of a synopsis here, so....
Here's the plot: Some guy is getting married to some gal. The guy, deciding to be a philanthropist for no reason in particular, resolves to make the whole village love each other. He does this by contacting a sorcerer to brew him up a love potion, which he feeds to, yes, the whole village. Unsurprisingly to anyone who's ever seen or heard of any other story that ever even mentions the phrase "love potion", it doesn't work out the way he'd hoped. Everyone falls in love with the wrong person. The sorcerer, unwillingly in love with the heroine mentioned in the first sentence of this synopsis, reveals that the only way to reverse the potion is for either the hero or the sorcerer to die. The hero has to stick around to get married, so the sorcerer agrees to sacrifice himself. The final scene shows all the correct couples happily dancing while the sorcerer dies.
On the whole, I liked it. It was funny, and there were some good songs in it (http://www.youtube.com/watch?v=qTF11YTIuic). The ending, however, could have been a lot better. The sorcerer was the kindest, most level-headed, and the funniest, so he was the best character by far. Not only that, but (and here's the point of my post) there was a fairly obvious, fairly clever, and much better ending.
You see, when the sorcerer is selling the potion, he explains that it has no effect whatsoever on married couples, since it's made with the "strictest of principles". Told you he was nice. But this little fact is just a joke that never comes up afterwards. I think that it's a loophole in the potion. The play should have ended with all the wrong people marrying each other, and the potion's effects stopping soon after. Granted, that does leave the village with a morbid divorce rate, so it would also be a good idea to throw in a twist of the preacher not being legitimate, but still enough to break the curse, but that wouldn't be too hard. Not only is there a better ending, but it can even be found foreshadowed in the play.
But this does give me an idea for a musical... I can have a love potion with effects that will leave once the people marry, together with a sideplot about a criminal disguised as a preacher. I just need to be sure that I'm different enough from The Sorcerer that I won't be accused of copying.