I liked the story, it’s fast paced, the characters are an interesting bunch, and they interact well together. The back and forth between Escobar and Walken for instance.
I can see that there’s a character arc problem, because there isn’t one. At the start Escobar gets doped with a lot of stuff. He has no fear and no emotional attachments to speak of. So he goes through the story as a robot. He sees things, he notes them, but because his emotions are dampened they have no effect until the very end when the stuff wears off.
When the stuff finally does wear off it’s the emotional discharge talking and not really him. He probably thought similar after the Philadelphia incident, an augmented survivor’s guilt.
The end is also a bit of an anti-climax. After all that’s happened Escobar finds the enemy leader and it’s Jimmy. Who is Jimmy and why should we care? Other than a few tidbits of something bad happening in Philadelphia we know nothing of Jimmy except that he’s believed to have died there (in fact, before the ‘big reveal’ he’s only mentioned in two sentences).
Jimmy does things for greed, because he needs more suits. They must be worth an awful lot, because staging such an operation can’t be cheap. Where does the money come from, and the troops? Aren’t there other ways to get them? And why won’t the customer take the suits he can get and just pay for those? A few suits are better than none at all.
In all I was expecting more and the enemy being Jimmy didn’t do it for me. There was no real emotional connection to that character. It also ended rather abruptly, Jimmy’s already as good as dead when Escobar realizes it’s him. There is no conflict (loyalties, friendship, the thermite) because his gun already took care of it, so he can only complete the mission and be done with it.
As for the setting, you mention that: “The tenements were mile-square buildings, each their own little community, with banks, grocery stores, schools, churches, and everything else inside. Each building whipping by was a self-contained city.”
I’m not getting the sense of the building being all that large once they are in. It also reads like a pretty generic office-type skyscraper. Where are the homes, the stores, the churches? If they are self-contained where are the food production facilities?
In the beginning there are a few hallways, then the hospital, and more hallways and stairwells. You can spice it up by showing more of the ‘self-contained city’.