you have a beta ready after 12.5 hours - thats the first problem.
I would hate to think how many hours a popular custom map would have spent on it - i would guess its more it regions of 100's
the brushwork dosent actually resemble anything that looks like a building/structure , the texturing is rushed /repetitive (floor tiles going up the walls), the skybox looks like a hl2 one, theres is very little lighting (black shadows everywhere)
thats the stuff i noticed anyway - having not released a map myself yet and being new to mapping/hammer in general.
on the positive side you have the basic concpets of maps design sorted now, my advice would be to go through the official maps the decompiled versions and even some of the better custom maps and see how they do things, its a great source of learning how to do stuff, so long as you dont just copy paste it

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The part about people playing it,
honestly people will seem to play anything in tf2 if someone else is already on a server - last night i fired up a test of 1 wall, i forgot id left my ports open so it was visible to the internet, after going afk for 10 minutes i tabbed back in to find 4 other players on the server having a grand battle over the 1 wall and 1 spawn point in the map
