I was just wondering if you'd given any thought to altering how attacks of opportunity currently function. I think they're great as they are, but have you considered implementing facing rules with them? Since you have flanking and backstabbing already, I think it would be great if there was some variation in the effectiveness of attacks of opportunity, depending on where the defender is located to the aggressor. For instance, if I move through someone's AOO area where they have their back to me the whole time, they should have a penalty to attacking me, or not be able to attack at all at say, a 45 degree angle with AoOs. This obviously wasn't how it was implemented in games like ToEE, but since you've adopted some rules that rely on facing, I don't see why this would be overlooked (Beyond the limited time and resources of Larian, obviously)
Some creatures like beholders would have a 360 degree AoO range, and you could have traits that limit/eliminate the blind spot from players.
