The story is simple - good guys on a train, bad guys board the train, and what follows is two hours of non-stop smash you brains out gratuitous violence. The characters are enjoyable to watch and chemistry is pretty good. I liked the bad guy even though he reminded me of Pauly Shore.
The story framework is quite simple but the story progresses in unexpected ways. It constantly adds to it so the story doesn't feel flat.
Yes, it has some flaws but doesn't leave you too much time to question anything. Just buy your popcorn and go for it.
I recommend this as great entertainment but you can't be squeamish.