Content
The screenshot seems to show off a lot of the map, which is a good thing. The description is fine also.

Theme
The theme is very original. Yet I would think the war-part is a little too much to reach this time, it still is being showed off quiet good.

Texturing
The illusion of having the train be in constant motion while it isn't because of texscroll and some geometry bugging, hasn't been done a lot before in gameplay maps. It's something which makes this map pretty unique.
The only thing which still reveals the train isn't in motion at all, is the specular- and envmapped-based shaders (especially on those trucks).
Nice to see the shader back again, but don't forget; it causes rendering trouble when people using glsl rendering path instead of the default OpenGL/Assembly.
The texturing in overall isn't that great though, as the war-train has very jolly colours for supposing to go to a war-zone (or departing).

Geometry
The geometry is done pretty good. You still could skytexture surfaces which players aren't able to see, as in details like parts of the vehicles, etc.
If you would fill the outside of the map with geometry, the skytextured surfaces will disappear, which solves the flickering skytexture bug when being outside the map (as the engine thinks it should display the inside of the map also).

Lighting
The lighting is a little odd to me, as it's too bright. When your in a tunnel, it often is pretty dark with just some certain places lighted. In other words; play with the ambient some more to get more contrast between shadows and lighted areas.

Detailing
The detailing is pretty good. I like the models you've added, yet they aren't that great for their purposes. They could also be packaged way better, as the flag-marks (and probably some other models also) can share their masks and meshes.

Clipping/Noclipping
The clipping seems to be fine, nothing to say about that.

Flow
The flow is fine outside the train, but being inside one of wagons is a pain. You hit your head against the ceiling everytime you jump and also when you want to jump into the wagons. Be sure to make them some higher.

Gameplay
The pickups could be placed some better. They are very concentrated and overall, in a very small number for the size of the map. Be sure to positioned some better and add more of them.
Even it's a nice concept, the fact the layout is very straight kills the idea of having very competitive matches. Having several trains together could fix that, but then the trains should be way more optimized as the map already counts more as 100k of wtr.

Overall
It's originality is it's strongest point, but be sure not to concentrate just on that only. 5/10 for now.

It may be just texture scrolling and geometry glitching, but the effect initially is very convincing. Standing and watching the train go by you is very cool. The actual flow of the level and such could be improved, but I do like it's originality as it is, too. A more cramped space can be good for a small number of people, as you have suggested. This map will never end up playing like a normal map because of its design, but the difference is good in my opinion.
Plus it's a train, and I like trains.