I updated my enemies with a simple behaviour:

• defensive will hide when hit once,
• balanced hides when too much damage is taken,
• agressive doesn’t care,
• if ammo clip is empty hide and reload

The enemy has several states which it can use:

• Spawned,
• Run,
• Hide,
• FindCover,
• FindPlayer,
• Shoot,
• Dead

With this there is already some sort of behaviour to the enemy which already helps the level to be more interesting.