I'm not sure that Valley Metro Rail would be great for commuting on a daily basis because the way its designed, with the fact that it stops not just at every station, but also for every red light means that it takes about twice as long as driving, or even taking the bus to get to your destination.
However, to get to sporting events or activities in Downtown Phoenix or Tempe, Valley Metro Rail is a great way to go. You get to ride on a nice clean train, when there's a special event you're always riding with other people going to the same place, and you avoid the hassle of searching for a parking spot and then paying $20-30 to use it.
So if you're headed to Downtown Phoenix or Tempe, consider riding the rail. You'll enjoy it!