The light rail is great. I ride it 3 or 4 times a week. It's cheap transportation with air conditioning and free entertainment. Most people will leave you alone, but public transportation is open to everyone so you will sometimes run into interesting characters. I usually listen to music, play with FB on my phone or read for class.
It's definitely a more crowded commute when there's a Diamondbacks or Suns game, between the 9-5 travel "rush hours" and during the school year. In the summer, it's pretty empty. I took my bike on the train without a problem all summer long, but I find it's sometimes too crowded to bring my bike with me during the school year (ASU mostly, but there are other high school kids on it sometimes, too.) It only stops in certain cities from the Mesa/Tempe border to North Phoenix, at this point, but there are plans for expansion. If you happen to be attending an event at US Airways Center, you can ride the light rail for free with your ticket stub. Watch out though, meter maids hop on and off the trains checking for train tickets. I see them once or twice a week.You sometimes see homeless people duck off the train when they get on. Oh wells. It happens. And my favorite part is that Valley Metro likes to use social media! Use the twitter handle @METROrail. They usually respond back!