The Westside Express Service, or WES Commuter Rail, is a rail line ran by Tri-Met that runs between Wilsonville and Beaverton. It is separate from Tri-Met's MAX light rail service, being a full heavy train, running on regular rail tracks.
The line opened recently, in February 2009, and took a relatively small time to complete after the politics had been completed. The rails were already in place, and since it was a commuter rail line, it only has five stations, so there was not too much construction to be done---especially in comparison with the Westside Max, which involved tunneling many miles through a hillside. There were some problems when the manufacturer of the engines fell into bankruptcy, but these didn't stop the trains from being delivered.
I had the pleasure to take a trip on the line the other day, and I found it to be very enjoyable. The train feels like taking a train, in comparison to riding a light rail line, which feels more like riding a really big bus. The train is much more spacious, travels higher above the surrounding terrain, and has much fewer stops. For these reasons, I don't feel that I was the only person taking the train for less than utilitarian reasons.
How successful the line will be after the initial excitement has worn off remains to be seen. How much of a demand for transit service there is in Portland's wealthy southwestern suburbs is a big question. I get the feeling that in some way the rail line, which is more comfortable and glamorous than riding a bus, was designed to lure suburban commuters who would otherwise not consider transit into hooking into the Tri-Met system. Whether this will happen remains to be seen.