To me the most important thing a SS does is field. They set the defensive tone on the infield much like the centerfielder does in the OF. Anderson has had a great last couple of months at SS after getting off to a slow start. He is also giving us a great baserunning addition as well, ranking 6th of all SS's. His RC+ is 91 as of today, so while below average, it is still not awful. That even ranks 16th amongst all SS's which again, is right smack in the middle.
As of today if you are looking at the whole package, he is quite literally the definition of a middle of the pack SS, with the time to become a top 10 guy pretty easily.