McGeary is having an interesting year. After dominating the leagues that he was too old for, he started off well in AA, only to slump quite a bit as the pitchers made adjustments to him. But in the last couple of weeks, he has quietly come back a bit, lifting his average about 50 points while still showing power. That is exactly the kind of performance that you want in a rookie.
He has a long way to go, both in performance and in experience, before I would consider him to be a very good prospect, but so far, he has shown not only the tools, but the talent to succeed. It is possible that he will never be anything more than a DH, but the Cubs, last in baseball in DH performance, shouldn't be quick to discount that.