To say that I thought the plot was predictable would be an understatement. But to say I didn't enjoy watching the movie would be a lie. It has some graphic scenes mind you (and while you might have seen better special effects, this still can be called gruesome at times), so it is not for the squeamish.
There's not a lot of plot involved in the story, but I still will not say anything about that. You shouldn't care too much about it anyway and let the underdog story carry you through it. You'll understand my summary line too (especially if you have seen a movie I'm obviously referring, though this is of course a somewhat adult version of that). All in all a decent thriller movie, that can be entertaining