I use the epic rules, and other than ES, I haven't really had a problem with them. The rulebook wording, OTOH... I think they needed more editors, not more playtesters.
ciaran: Your save rules favor spellcasters too much. The 3.5 designers were smart enough to realize that a 50/50 chance of beating an opponent's Will save is too great; that gives a caster better than even odds of ending any encounter with a single spell! No risk, no melee engagement, and not even clever save targeting; your foe drops right away. That is not consistent with the CR system, since one action and one spell hardly represent 20% of a single spellcaster's resources, let alone the party's.
If anything, epic save progression tends to even the odds somewhat for classes with generally crappy saves (like fighters), who are seriously left behind on their weak saves by about 20th level. But really, how bad is the +1/2 save progression? Let's investigate. A Wiz40 with SF, GSF, and ESF who spends 6 of his 13 epic feats on ISC and has an Int of 48 (not unreasonable at this level) will have a save DC of 48 with his highest-level spells if we assume that ESF was nerfed for 3.5 (although the designers didn't actually make the change, oddly). A 40th-level PC has a strong base save of +22 and a weak save of +16. Assume a base save-relevant ability score (Dex, Con, Wis) of 30 , a +5 resistance item, a +5 luck item, and a relevant save feat (GF, IW, LR). That yields a +44 save bonus with the good save, +38 with the bad save. Given that the wizard can force two saves per round at least, he can cause his target to fail a save 24% of the time if he targets the good save, or 70% of the time if he targets the bad save. That's not bad for a one-round kill at distance.