So, this isn't bad for a first map!
But some little tips i wanna point out:
Many places, especially here, are quite over scaled. You can fix this by either making the geometry smaller, or adding certain things. Like buildings or more geometry. (In my opinion, adding is easier.)
Another thing, the pickups are placed in strange places, with not much of a reason.
You don't have many pickups, which could be a problem, but then you have one or two very powerful ones ones as seen here and the picture up there ^