I think the hit tool is average to below average at best, the power is about average, and the swing decisions are average at best and probably below average based on his general aggressiveness as a player. As a pure hitter in the box he probably ends up average at best with a very real chance to be below average.
His best offensive ability is his speed, but his baserunning skills aren't exactly refined, he's just very aggressive. I think his AVG, OBP, and SLG in the minors have been inflated by his excellent speed. Bunt hits, beating out grounders, taking an extra base on a hit etc. It still counts, but I think it hides some of his lack of skill in his actual hitting abilities at the plate if we just look at the stats.
Left-handed Corey Patterson isn't a bad comp, but PCA hopefully walks more. Like Patterson, the most value probably comes from the glove and wheels.