Concrete Jungle

Pretty basic, which can be easily forgiven since it's one of your very first maps. One thing I would say is that you should make sure you place info_nodes entities for AI pathing. Without info_nodes, enemies will tend to stop in place when they can no longer see the player. This means that the zombies in the first room will never follow you into the second. Likewise the assassins in the second room are severely handicapped since the player can hide behind cover and then peak and shoot to kill them far too easily. Another thing to note is that it doesn't really have any sense of place, it's literally two giant concrete rooms. Again, forgivable given the lack of experience. The next step is to make a map with interactive elements such as buttons, doors and triggers and so on. Once you've got the basics down, work on detailing to make believable environments.