I leave aside the specifics of the setting and additions from various books (races, classes from Complete series, BoEM, Book of Roguish Luck, Hallowed might, use of Chaositech etc etc) and precise that my game combines AE and D&D, with AE rules being the base (overrides D&D in case of contradictions: Keen + Imp. Critical stack, no favored classes, etc):
- d10 instead of d20 for Initiative rolls: less variables in initiative and more value for Improve Initiative feat.
- AC is rolled with d20 instead of "10": Players more active in their defence. More fun for everyone around the table and it doesn’t slow down combat in our experience.
- Action points from Eberron plus uses from Luck rules of Book of Roguish Luck for specific classes (Unfettered, Rogue, Assassin...) – a blend of action and luck points allows for more strategic choices from players. They are separated from Hero Points, which in our game are rare and used for well, truly heroic actions.
- Automatic failure on 1, Critical hit if critical threat reached (no confirmation check but AC roll can still overcome the hit for normal damage, and no damage on 20 – plus with home feats): This makes the combat much quicker, instant kills happen more often, overall gameplay is cinematic IME.
- Weapon Groups variant – because Exotic Weapon Proficiencies applying to just one precise weapon are just waste.
Plus maybe a few minor ones I forget at the moment.