Pros: Absolutely beautiful. From looking at payback, you've greatly improved, I can't stress that enough! The amount of details in this map is astonishing, and the map runs so smoothly. I foresee the next official community map. The map has inspired me and given me ideas for my map :P
Cons: I haven't found any real cons, which is great considering that this is still in beta, but there are some small things I'd like to point out:
I showed you this before, near the spawn the prop fading is a bit messed up. You are not able to view the pipe crossing until you get closer. Just a small fading problem, easy enough to fix.
A small crack in the displacements near the BLU spawn. It's right across, to the left of where I'm standing in the first image. If you need more clarification, I'll do my best :P
I have a feeling you might not be able to sew it, so just cover it up with a prop, it shouldn't affect it too much.
Prop shadows need to be disabled. You see the first screenshot? In the building to the left, right in front of the entrance.
These props should probably be fixed or removed. This is near the explosion, in a room at the top. There are no backfaces on the models, so they should only be placed against the wall or else it would just look odd.
This is the small side building right near the exit from RED spawn, at the end. Need to raise the displacements a bit
Improvements: Look at cons, that's all that's wrong with this map really.
Notes: I can't really comment on gameplay, as I have yet to play this map on a full sever. Once more people show up on yours, I'll join in and update this.
EDIT: Ok, I've played the map with other people on your server. The map is very fun to play. My only concern is the chokepoint you were talking about. That is a really bad one. My team was stuck there the entire time. Try adding more paths to get out from there. Some underground tunnels.