Peralta was the subject of Baseball Prospectus' Baseball Notebook today. Essentially, Peralta's having an historic offensive year for a shortstop his age. In fact, the last time a 23-year-old (or younger) shortstop had a season with an OPS+ above 122 was in 1996 (Alex Rodriguez).
The article also mentions Peralta's good showing in Prospectus' defensive metrics, although I don't completely buy that Peralta is as good as they say he is in the field. Jhonny doesn't have the range of, say, Julio Lugo, and although he has a good arm, it's not in the same league as Rafael Furcal's. But that's not the main reason why Peralta's been one of the best shortstops in baseball this season; his bat is. There's a possibility that he gets some talk in the AL MVP race given the position he plays and the Indians' winning record, but I don't think he has the name recognition or reputation to make voters pick him over an Alex Rodriguez or Vladamir Guerrero. I know, it's not fair, but given the media attention Cleveland gets and the laziness of some baseball writers ("Hey, who's this Peralta guy!"), I'll be shocked to see Jhonny finish in the top 5 of the MVP voting.
The article's free, by the way.