Have I mentioned that Martin is a really cool character? I could go into my reasons for this, at length, and probably will at some point. For now all I'll say is this: I was terrified that he was going to be Deckard Cain.
I swear. I was expecting some old guy, constantly giving me history lessons that I neither needed nor cared about. Instead, I got a guy who was (a) less annoying in combat than the town guard I'd just had to babysit and (b) inexplicably angry at me.
At first I thought it was just because I wasn't very good at aiming. Then I played through the scenario with a couple of characters, and discovered that, no, he's just constantly scowling through that first section.
So, I guess that's actually two basic reasons why I like Martin: Not Deckard Cain, and constant scowling. Two qualities you really can't go wrong with.