I thought it was one of the worse arcs because it completely overhauls the perception of his character.
It kind of was originally implied that Martin, always running away from his responsibility couldn't handle having Finn so he probably had ran away from his problems.
I enjoyed thinking he was always a shit person and that Finn had to unfortunately deal with him to find out anything about his origin or where the remaining humans were but he was always too much of a dick to answer him truthfully or at all.
In his last non-flashback appearance he states to Finn "No answer I give you will be satisfying." and I always took that, that he had no good answers or reasons that Finn would find comfort in (the fact that he just simply ran away from his problems) and at that moment Finn finally accepts that Martin is a lost cause and that Martin had already given up on himself long ago.
But nah. He used to be good but he got a nasty bump on his head which changed him entirely into the person he is.
Not that he was always shit but his bump made him a meanie.