There doesn't seem to be much in the way of level
design.
There seems to be little thought to spawn locations (are there even legitimate spawns?), combat hot spots (i see no choke or vantage points), related vertical combat (key TF2 gameplay component), basic aesthetics and related map theme.
A stereotypical first map "i don't know what i'm really doing, but here's something anyway" job.
I don't mean to sound like an arsehole but there
are a few things you will need to learn before releasing a map publicly.
First and for-most learn how to create a properly functioning spawn room, each map other than perhaps arena will require the whole spawn entity setup package; including respawn visualisers, resupply lockers, team filtered doors and class swap out trigger brush.
Later, learn how spawn location effects game speed, balance, and general playability. This will ensure an enjoyable map will be your final product. This is more a gameplay theory aspect when it comes to research (and experience) rather than a physical thing you can swap out or debug.
Learn your displacements and alpha blending function. A fundimental aspect of any Source based game, and even on other game engines. Learn to create natural looking terrain using the displacement feature and it will make the world of difference in your virtual environment. Even bad displacements can make your map look 10x better.
You might want to read this discussion on improving the quality of your camera view:
http://forums.tf2maps.net/showthread.php?t=6358&highlight=detail+hammer
It looks like you seriously need to increase the model draw distance, atleast.
Provide cover.
One of the things that makes a box map like this fundamentally "fail" is how basic and horrible the gameplay will function (and remains completely identical to any other map of this form). People spawn, spam in each others general direction, and die or live, 80% down to chance. Cover will normally come in the form of detail. But you'll still want to simulate basic cover in your early beta's to get a better response from player feedback. Otherwise responses can be vague, generic and varying from one perspective to another, in the terms of what should be implemented and how. In which case, you can never really lay claim original authorship after spitting out everyone elses idea's on such a rudimentary level.
It is hard when developing an arena map, particularly at such an early stage in experience, to avoid your box map situation. For all intents and purposes lumberyard is little more than a box map. But the variations in height, player paths and environmental hazards and map theme detracts from it's basic layout.