I've had this car for about a month now and I've ran up about 1100 miles on it. Each time I take it out to drive I like it a little bit more and I loved it when I bought it. The xB isn't the fastest, sportiest, or most luxurious car I've owned but it's pretty fun to drive, it handles well, and it has a comfortable ride whether I've been on road trips or just cruising around town. It's a nice balance in pretty much all fronts, which is surprising for a car this cheap. Also, the folks at Scion are a pleasure to deal with. I've also noticed that a lot of people complain about the fuel economy of the xB but I've found that I've gotten between 28 to 33 mph, which isn't that bad.
Balance of performance and comfort, interior roominess, amount of features for price, customizability, the way it feels like you're in a small SUV but not wrecking the environment. Pretty much everything.
Scion compromised too much with the exterior styling. There's something iconic about the first generation xB, the second gen xB is a great car but it doesn't turn heads the way that the original xB does.