The people who did not like the movie need to stick to action packed ones. This movies center piece was the mystery behind the main character. I was intrigued both times that I watched this movie, on the first watch I was following the plot, on the second watch I noticed more smaller details that added to the story.
The entire first half of the movie emphasizes the characters inability to focus, and his desperate attempt to stay functional. About half way through anyone who is paying attention would realize that this guy has lived for so long that he no longer wants to live and has chosen to live in solitude, he has outlived every friend he has ever made. He has become to regret the things he have done, all the people he has killed and has been trying to stay away from killing things.
Next bit is Spoiler but I felt the need to clear things up.
It seems that based on a few lines that the main character says, especially in his fit of rage in the end. He is being punished by God to walk the earth for eternity. If it isn't God then it is something close to it. He mentions how he is mentioned in the bible as Cain although his name at the time was something else but somewhat similar. And asked the mysterious presence that appears every so often if its because he killed Habal. If his name was mispronounced of misinterpreted from something else into Cain, in the Bible there are mentions of Cain murdering his brother Abel and being cursed. Some tidbit info that isn't confirmed but lines up with what was shown in the movie :)