This is quite nice for a first attempt at mapping. Great job! I loved all the little details and how the maps areas connected together. There was a lot of detail that didn't rely on an over abudance of sectors.
Other than some of the icicle textures not showing on the back side, I didn't see anything off. If you're looking to make the fights harder, I advise stricter control over ammo, as you can walk into the last fight with 600 plasma and an abundance of rockets I was expecting about twice as much opposition. But don't feel like you're doing something wrong if the map isn't hard: there's absolutely nothing wrong at all with a map thats on the easier side.
Overall its ridiculously clean for a first attempt at mapping. You should be proud and definitely keep mapping, you'll make even greater things if you do!