The thing about Martinez is, he is just a natural hitter. The kid won batting crowns in the minors and will vie for them in the majors as well. He has a short, quick, swing, which should mean he is a consistent .300 hitter starting this year I would wager.
Perhaps this area that surprised me the most was his power, and not just his HR's. He had 38 doubles, and I would guess a third of them were peppered off the OF walls, minimum. This is probably the best indicator of future HR increases, so do not be surprised if he becomes a 35 HR hitter sometime soon.
The best part of it is, his power is independent of his average. Many -maybe even most - hitters have their average decline when their power goes up or vice-versa. This is not the case with Martinez. You may be looking at a .320 hitter with 35+ power when it is all said and done.
I have him at something like .310 with 28 HR's or so, which could be a little low but I doubt if he will be that high.