Just checking.
Was it just our group, but at playtesting we really missed clear rules for Attacks of Opportunity.
Our DM called that because there are no rules, there are no Attacks of Opportunity.
Made a lot of combats really weird.
Sound Familiar?
Yes, as in no attacks of opportunity just doesn't work.
I understand the thought that opportunity attacks slow down the game but actually, when you do damage during an opportunity attack that speeds up the game.
Nobody should ever step away from a dangerous opponent without provoking an opportunity attack.
You're not going to speed past a fighter without him or her taking a swing at you. If you really want to get to that wizard, you're going to have to pay some blood.
And we need opportunity attacks to make some of the popular feats still useful such as point blank firing and quick drawing of a ranged weapon.
Furthermore, Dodge Action could be so much more useful if you extended that to opportunity attacks and defending your allies with them.
You don't actually need AoOs. What you need is something to stop people just walking past other people. If your movement stopped when you engaged someone that would work almost as well - it would just lower the risk calculation.
I don't like the 3.X AoO rules and would much rather replace them with the 4e OA rules - which are stripped down to the bare essentials. In short the 4e rules say "No running past enemies and no making ranged attacks in melee unless you want to suffer an AoO".
No need for the tactical schmucks to worry about whether drawing a weapon, quaffing a potion, or standing up from prone provokes an AoO. They don't. It's just walking past the enemy and shooting a bow or a ranged spell when someone is right in your face. These are clearly explainable as bad plans and even the tactical schmucks get that.
And the positioning OA rules are more than enough to keep the tactical gonks happy as long as the DM isn't a complete tactical schmuck. Especially when combined with 4e defenders where when you provoke a marked target they may get a free swing at you - but the fighter gets a free swing at them. Or with the Prime Shot rules where you get a bonus to hit for being nearest (or joint nearest) to the enemy if you're using a ranged attack - so walk up to them, prime shot, and if the enemy shoots you the fighter cuts them open.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.