|OK, sorry this took me so long...
First off: things you did well.
You have a very clear story, and a good understanding of the setting this all takes place in. You're obviously familiar with Resident Evil, and you've got a very detailed idea of how everything goes in your story. You did a good job of considering realism, choosing actual guns, remembering that ammo is a finite resource, and taking into account the surroundings on a train (luggage and so on). This is a good intro, it starts just before the action gets going, and leaves you room to go over back-story, without leaving the reader feeling confused about what's happening.
Secondly: things you could improve.
The first thing I would suggest, is considering why you've chosen 2nd person for your perspective. 2nd person can be very difficulty to write, and often would be more impactful if switched for 1st person. I think that this is the case here, telling the story in first person would seem a little more natural and allow for easier character development. I think what you're going for is the feel of the games, getting the reader directly involved in the experience; if that's the case, I could see 2nd person working well, but would include more emotional information (when you're scared, or nervous, or surpised).
Also, though your description is detailed, it feels a lot more like you're just telling us what's around, rather than really describing it. I would suggest stronger imagery, and maybe combining certain sentences together to improve the flow. Example: instead of "You asked Niel to help you get through a hole in the top of the cabin. As you get out you find tons of zombies all around before you help Niel up you shoot them off the train. Most of them stumbled when shot which meant they fell of but others had to be shot in the head." try something like "As Niel boosts you through the hole in the ceiling, you see a horde of undead crowding the roof of the cabin. Before pulling Niel up behind you, you turn and open fire on the zombies. Most of those you hit stumble, falling off the train; but some struggle on, until a well aimed head-shot finishes them off." See how that flows more smoothly, and implants a more vivid picture in your mind?
Your tenses (past-present) sometimes get confused as well, jumping back and forth between describing this as having happened and currently happening. I suggest sticking purely with present tense, as though this is all just happening. That is if you stick with 2nd person perspective, if you switch to 1st person I recommend past tense.
Lastly, your dialogue will be easier to read if you separate it from the rest of the paragraph; giving speech it's own line makes it stand out and it's easier to keep track of. Also, review punctuation for dialogue; commas instead of periods at the end and all that. It's not too big a deal, but it does detract somewhat from the writing. Getting someone to help edit will clear up this stuff, as well as some of the other grammatical errors you have.
I know that in comparison to 'things you did well' the improvements look like a lot... But don't get discouraged. This story has a lot of potential, it's well constructed and clearly thought out. A little polishing and revision will make it great, and help your overall skills as a writer. Revision is what makes all great writers more than simply good. And I can't stress enough: KEEP WRITING! Keep up the good work, and then keep trying to make it great work.
It was an interesting read, and I definitely want to read more of your story. Hope I was helpful. Let me know when you next want a review!