Martin is not a finished product, nor is he a sure thing to stick in the rotation, however he does have a big league arm. His fastball can get into the mid-90s range, and he's obviously been tough to hit this season. His last two starts were both six innings of no run ball, and he surrendered just 7 hits in those innings. His biggest issue, his control, is still an issue, as he walked 3 in both of those games, but he's done better of late. Martin gets into trouble when he doesn't throw strikes, like many other young arms. If he can get over that, I could see him topping out in the middle of the rotation, but I'd still bet he ends up in the bullpen, at the back-end.
Either way, welcome to Philly, and let's hope he sticks for a long time!