First, go to the TKTS booth and get the half-off tickets. Unless it was for the original Producers, Hairspray, or Mamma Mia, you should never pay full price for the tickets. Also, I have yet to encounter a line at the downtown TKTS booth (in contrast to that long line in Times Square, where it always seems to rain). Second, I might give something away, so if you haven't seen the show, perhaps you shouldn't read this review.
Now, about Urinetown. In order to prove its point, Urinetown needed to find something that we couldn't live without (water and peeing), and then decided to make a musical out of it. The show is about a bad businessman who makes the poor people pay to pee. This of course makes the poor people who can't afford to pee to illegally pee in public, whereupon the charismatic cops (who you really like until...) catch and send these vagrants to Urinetown. Being sent to Urinetown means being thrown off a building and plummeting to your death. The daughter of our bad businessman falls in love with the leader of the rebellion (who gets thrown off the building), joins the rebellion and has her father thrown off the building.
The big twist in the end is that the bad businessman really saved the lives of everyone in the city because he regulated the water supply. And the idealistic daughter accidentally ended up killing everyone in the city through the mismanagement of the limited water supply. Although the premise of Urinetown is ludicrous, it is highly entertaining. Plus, you can choose to laugh and leave being entertained, or you can dissect and think about the themes that are brought out about good versus evil, about idealism versus realism and business, and about poor versus rich.
This is not an expensive production and there's no fancy costumes, but it's very entertaining.