Throughout the map I notice it used portals:
These work really well, because they stick out from the rest of the map. With the use of the teleporter, it makes the map seem bigger than it is.
This was the next big thing I noticed; A bridge. This bridge may look useful and it is, but by using it you make yourself seen and you can be kill from behind, however the bridge gives you the opportunity to sneak attack enemies. In short it is a risk and reward level design.
This is the next good level design. This floor can be shot from and by doing so gives you easy kills and the enemy will not know what happened (unless they know about the floor area), however someone can sneak up on you and kill you, because you are looking downwards. Another risk and reward level design.
This is an underwater entrance. This is to reward players that are adventurist by giving them a shortcut to a certain area or access to an exclusive area. Just by adding an entrance underground, it makes a game more re-playable and enjoyable, while adding in more strategy to the game.