Looks like a nice! The paths seem a little long. I'd have to play it with people to get a better idea of how it feels, but consider rotating the base exit 90 degrees and cutting out most of that wrap around path. I feel like it's going to be a lot of traversal with no action.
The flag platform does allow you to double jump up to the back path, but it's pretty difficult. I'm guessing that route isn't intentional (without the help of a teammate). If it is, I'd suggest a ladder or something for more casual players. If not, you might want to make the platform flush with the ground to avoid that.
Using _sun_surface will get you much more natural lighting than _sun_ambient + _sun_diffuse.
On the minor detail side: Some of the crate textures are misaligned, and all of the barrel textures are upside-down. You might want to add some ramped or stepped clip brushes next to the sideways barrels so you don't stop when trying to walk over them.
