I'm about to go to bed, so I'll only give feedback based on the screenshots you provided, but:
Generally, I like the map, and I think you should be proud of it as your first finished map! The first map I published for HL2DM was pretty uninspiring... And didn't work.

You've done well!
Firstly: You're using a lot of HL2 textures. In
this screenshot, you're only actually using about 3-4 TF2 textures, and about 4-6 HL2 textures (e.g. the metal vent texs on the sides of the box in center view; the metal girder tex on the bridge; the metal tex around the doorway with the red light at top right). You should avoid using these in your maps, because 1) it detracts from TF2's clean artistic style and colour pallets, and 2) because if the user doesn't have HL2 installed, they may not be able to see the texture at all.
Secondly: There's not a huge level of detail. Granted, this is your first map, but it's fairly obvious that there are differences in the level of detail between
this screenshot from your map, and
this screenshot from cp_gorge. Adding in decals, making more complicated brushwork, and trying to give the map a bit more of a backstory and ambiance. It's hard to say exactly what to do and how to do it in terms of adding detail, but it should all be theme-relevant and cut out any blank walls.
Those are just the brief comments I'll make so you can take your map further. It's a good starting point, and you should be proud, as I said!
The best way that I found to learn how the best maps are made was to actually go into the map and look at the brushwork and layout. You can find them all decompiled for you to poke about in
here. Learn from the best! Good luck.
Edit Sorry, I was looking at your old release thread. I'll leave the links to the screenshot tumbnails in for legacy.
In the second screenshot from the top, the floor of the bridge with the big metal pillar on it is definitely a HL22 texture, I'm almost certain. I could be wrong about the other textures, I mentioned before, but I've used this in HL2 maps before.
Another thing I meant to say was that screenshots look much nicer without the GUI in the way.
Open the developer's console, and type in "sv_cheats 1" then "cl_drawhud 0". It'll hide it for you.