I don't like or use the epic rules so I won't deal with those feats, but you left off quite a few prerequisites from nearly every feat (maybe you were just in a hurry, but I think all prerequisites need to be mentioned).
Taking the advice Crothian gave, I added Str and Dex requirements also:
Combination Attack: Power Attack, Combat Reflexes, BAB +8, Str 13+, Dex 15+
Improved Combination Attack: Power Attack, Cleave, Combination Attack, Combat Reflexes, BAB +12, Str 15+, Dex 17+
Greater Combination Attack: Power Attack, Cleave, Great Cleave, Combination Attack, Improved Combination Attack, Combat Reflexes, BAB +16, Str 17+, Dex 19+
Powerful Combination Attack: Power Attack, Cleave, Combination Attack, Combat Reflexes, BAB +12, Str 17+, Dex 15+
Combination Critical Attack: Power Attack, Cleave, Combination Attack, Combat Reflexes, BAB +16, Str 19+, Dex 17+
I am still not sure I would allow these in my game. Giving extra normal attacks for AoO and a natural 20 seems like too much benefit. The crit is already there and these feats do not get rid of it; and against creatures immune to crits, these feats give more than normal attacks, thus more damage, thus sort of a get-around the immune-to-crits ability. If I were to use any of them, it would probably be only the first one: one extra attack per round is powerful, Cleave is another way to get an extra attack (and is a required feat for all the rest of them). I would be more inclined to allow these feats if they did not require the most powerful of the fighter feats but rather some of the lesser used ones instead, so that the fighter is actually giving up something to get these. As it stands, such a fighter is able to get an extra attack every time an opponent falls, and whenever he rolls a 20. I suppose that these extra attacks would also apply to any AoO that such a fighter takes: AoO that cleric for casting a spell, roll a 20, get another, cleric falls, get another, that guy falls, get another, roll a 20, get another...
Ciao
Dave