Looks ok for your first map and first beta.
All in all I think the map is too dark. The stairs are black. There're light texture, but they doesn't light.
I'd also use a nice sun lighting for the upper floor, because you're already using a sky. Try to add something like this to the worldspawn:
"sky" "pbsky1"
"_sun_light" "250"
"_sun_angle" "198 -65"
"_sun_ambient" "30"
"_sun_diffuse" "60"
You also don't need a flag if there's no base and your map only supports the gamemode DM.
Nice to see that you added "angle" "#" to the player spawns.
Most of the barrels are well done, too. Just some of the top textures are misaligned and need to be fixed.
Some screenshots...
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Red: Avoid overlapping brushes to fix the different textures here.
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Red: Avoid overlapping brushes to fix the different textures here.
Blue: Cut out the blue area that all 4 corners are the same.
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Red: Avoid overlapping brushes to fix the different textures here.
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Red: Add clip brushes next to the light textures.
Blue: Rotate this face. Press "s" to open the surface settings, set a value at "R" and click "Apply Face/Brush" to rotate textures.
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Red: Rotate this, too.
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Red: Rotate this, too.
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Red: Rotate these, too.
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Red: Remove the edges.
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Red: Remove the edges, too.
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Red: Remove this edge, too.
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Red: Make the stairs a little bit more wide/narrow, that they fit with the wall and a player can't jump under the upper stairs.
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Red: Remove this edge, too.
Map is online @ [OTB] Beta! Let me know if you need the login to change the map.