A lot of slopes on the walls that are clearly designed for aesthetic purposes are exploited by humans to "jump" up and avoid the aliens, effectively giving them unlimited jumping. Well, if that was intentional, then they would have been given infinite stamina. As it is now, they can use stamina for sprinting and the walls for jumping, making it far too hard for the average alien to fight back.
Also, many ground slopes such as on atcs are abused to avoid headshots, which might make sense within the engine, but is neither realistic nor balanced. This should be changed. As it is now, dretches can only headshot absolute newbies.