In my opinion there are too little difference between difficulty options in the game. Personally I found the game to be a bit easy, even after turning it up to the highest difficulty setting. Here are a few suggestions on how to make the game more difficult on the higher difficulties.
Knowing where the enemy is at all times is the main reason the game is easy.
- No enemy positions should appear on the map before you have spotted them (red or purple blobs), unless you have specific intel. Even then their position should be less accurate.
- No red circle above the head of spotted enemies in the 3D world, only on the mini map. It's too easy to just shoot enemies accurately through bushes and cover when you can't see the actual person, but can see the red circle above their head.
- Spotted enemy dots on the map should fade after some time when you don't have direct line of sight of them. It's too easy to know exactly when they are coming around the corner as it is.
- Remove the hitmarker (the X and audio feedback when your bullets hit someone). It's annoying, and removes the uncertainty of whether or not you actually killed an enemy you can't see properly. Not knowing affects how you play.
- Don't have my character yell out "Clear!" when there is no way for her to know there are no more enemies left in the area. This takes away from the excitement of actually clearing out a room/area. Rather give us an option to manually have our characters yell out these lines when we think it's clear.
- Don't make it obvious if you are spotted. Remove the HUD and audio warnings. If someone walks up behind you and spots you, you shouldn't know until they start yelling or shooting.
That's all I can think of at the moment. Feel free to add to this.