Guild Wars 2

Have NPC foe aggro range increase when aggro’d if it is an aggressive foe. After losing aggro, the aggro range radius would decrease to a mid aggro range. After awhile it would decrease to normal. Then after a long while it would decrease to it’s lowest, which is only slightly smaller than it’s normal range.
Timid or defensive foes would have a fear range that would function in the same way as an aggro range, except in this fear range, the foe would evade the player when in range instead of pursue the player.
Also when foes are aggro’d, there should be some cue like an exclamation mark near it’s head that would indicate to the player that the foe has been aggro’d. An asterisk mark could denote fear in a retreating foe.

Also, i line of sight might add a little more bit of realism and strategy to foes. Instead of a circle around the foe, a frontal pie or cone shaped line of sight aggro range could be put in placed or added in addition. This line of sight range could widen or narrow down as a result of engagement also. It could also change directions also, based on head movement of the foe. Foes could scan the area moving their head left to right etc, adjusting their line of sight accordingly as they do so. More tactical gameplay could be had from this type of aggro as a result of this. This line of sight should be visible to the player to allow players to see this LOS and provide more gameplay. More difficult areas could have non-visible LOS to increase gameplay difficulty.