This location is a very good example for what a Starbucks should be. Usually, the service is good and timely, even if you go during a rush in the afternoon. The wifi can be hit or miss depending on how many people are using it.
The reason for the four star rating is the problem that is common to most State St/Campus open areas - the transient/homeless population. It's not unusual for one table to be taken up by someone's plastic bags or someone to be sitting out panhandling. It's not Starbuck's fault - you see that at most coffee shops in the area. There's really not much they can do to control the problem, short of kicking them out. That's an issue for the city of Madison to deal with.