I read very negative reviews of this system from 2009 to 2011, but suddenly they all got positive. I wonder what Yelp is doing with the reviews... or did the light rail suddenly 'get better' all on its own. Here's an honest, sober review from someone with a lot of experience taking public transport all over the world.
Light rail, like most public transportation in America, is a waste of time and money and provides 'services' only to the homeless. I've ridden light rail/trams and metros throughout the world, from Poland to Tokyo to the NYC subway to other cities in America, like San Jose, San Diego, and Seattle.
A stop near the airport is actually pretty convenient (although there's no reason it couldn't stop AT the airport instead of near it). So you can get to Chase field pretty cheaply and quickly from the airport, as I did to catch the DBacks. The ride was smooth, although through a very ghetto part of town.
However, what really ruins it are the large amount of vagrants who are actually quite menacing. Phoenix has a lot more homeless than I thought it would and the light rail is their mobile air conditioning shelter. There are rarely inspectors as far as I can see... this system really makes it worse. I would be afraid and ashamed to take my wife and children on this thing. Thank god for Uber.