Untitled Superhero Novel Thingy

Before we get started, I want to tell you that I noticed you've posted many of your own stories, but you've only actually done ten reviews. Remember to keep up with the review-to-post ratio of 2:1. It just ensures everyone gets reviews.

Thank you, Socrates. Stephen pushed his plate away

This is a joke, right? You just told us this guy inside the main character's head is named Glenn, so it still hasn't completely sunk in. I knew pretty quickly it was a joke, but some may not, so it would be better if you did something like...
Thanks, Socrates, Stephen thought sarcastically. He pushed his plate away
It's just a little thing, but it makes the joke stand out more.

By the way, I loved your description of the diner. Very well done.

pushing it open with a rush of cool autumn mountain air to greet him.

Commas after "cool" and "Autumn". Since "cool", "autumn", and "mountain" all describe "air", you need to separate them with commas. You do this whenever there are two or more words describing the same thing.

For a few moments, still more bullets dig into the front of the diner and its now-closed door.

Change "dig" to "dug". Remember to keep it past tense.

Government-job-God’s arm had apparently gone slack at the sight of him

I'm not sure what you mean by "Government-job-God's arm". At first I thought it was like some kind of governmental faction or something, but after looking at it for a while and reading on, I'm beginning to think it's the guy with the megaphone. Am I right? This is the first time you refer to him as "government-job-god", so when you use it in the possessive form, I got confused. You should either call him by another name or clarify who this is.

, the old cliché

This isn't part of the critique, but a question. How do you get the accent over the "e" in "cliche". I've always wanted to know... Well, back to the story.

I just noticed something. You put two spaces after your periods before beginning a new sentence. Your only supposed to have one. Just something I thought you should know.

Its blade was almost three feet long, the hilt bathed in the same dark shade of red.

This would be fine if you'd mentioned the shade of red earlier in the sentence. I know what you're talking about, but you still need to specify where the shad is from. Maybe...
"the hilt bathed int he same dark shade of red as his armor" or something else. Whatever you can think of.

Bullets ricocheted off of his armor and the pavement, howling away into diner behind him or the empty air around him.

Change "or" to "and". Saying "or" means that it's one or the other, not both.

Stephen hit the ground on one knee, skidded a few feet, regained his feet,

Watch out for the repetition of "feet". Change the last part to "regained his footing".

Stephen leapt over the median, making the other side and running for the far side of the road and the steep, rocky slope beyond.

This sentence felt a little off. Maybe separating it some would do the trick.

Stephen didn’t even feel the bullets as the fell away from his armor in a shining spray

Change "the" to "they".

There were two military helicopters behind him, both of them firing adding their guns to the one-target assault.

Comma after "firing".

and four missiles streaked forwards like magic

Change "forwards" to "forward". It works better.

Well... That was great! I loved it! It was very action packed and I like how it changed on a dime from a nice, small-town diner setting to a full-blown fight/chase scene with soldiers, firing machine guns, helicopters, rockets, and so on. Very well done. The only recurring problems I could really see was that you would sometimes try and fit too much into one sentence. Otherwise remember that there's only one space between sentences and you should be fine. Good luck with the rest of this!