Aesthetically, it's a nice looking map. The map took my attention at the first glance.
I must admit that the overall architecture, detail and design work are just (literally) perfect.
The railyway bridge is one of a nice piece of work, in my opinion. The displacement of the walls and ground is done very well. Really liked it.
As for the gameplay, it's basically balanced. The covering spots are sufficient, however, I felt that you could add a few more props here and there for extra covering.
The overall lighting looks just fine. One of the key features of this map is obviously its good ambience.
Despite of the fact that you used like two textures for the most parts of the map, the texture work seems just okay.
Now, there are a few aspects of the map that you need to pay attention to. Here they are.
I. The overall approximate WPoly count is 3000+, a bit high depending on the Goldsource engine. Though, the gameplay is smooth enough to cope with it.
Since, I don't really see any complex brushwork in there, except for the bridge of course, I believe that there are two main reasons as why the WPoly is high like this. I have mentioned them below.
II. From what I have noticed, roughly 60% of the map needs to be textured with BEVEL/NULL, as you left out almost the entire map with normal textures. This is one of the reasons why there is a lot of WPoly count. Since, the main gameplay is concerned with the ground level, you don't need to apply normal textures on those parts which players normally can't see.
III. Similarly, there are a lot of objects in the map that need to be tied with Func_Detail/Func_Wall to reduce the WPoly count as they aren't utilized for the VIS optimization purpose and are just only details.
For instance, this staircase. You can clearly see the staircase is dividing other solids unnecessarily.
Here's another example. As you can see the displacement you created is causing unnecessary divisions. To overcome this issue, simply convert it into Func_Wall/Func_Detail.
This is the second reason why there is a lot of WPoly count.
I believe these are the only major defects in this map to worry about and you can overcome them simply.
Just my personal opinion here, you may add a little fog effect to achieve some extra nice atmosphere overall.
Before I conclude my review, I just have some pieces of advice for you, hope you will find these useful.
I. When you start creating a level, try to always use temporary textures such as DEV textures or BEVEL/NULL. Though, I highly recommend using either BEVEL or NULL so that you will only need to apply textures on those parts which players can see, rest will not be rendered in-game.
II. Props and objects which don't block player's view significantly should be tied with either Func_Wall or Func_Detail to reduce the WPoly count. Examples may include small crates, pillars, arches, barrels, etc.
That's all I have to say about your map. As I said earlier, the maps looks perfect in its aesthetic terms, but technically there are a few things to look into.
Feel free to ask any question related to this. Good luck! :)