Extra actions can pretty much break the game. In 3.0, Haste was at least readily available since it was a low level spell, thus avoiding breaking the game AGAIN via assymetric extra actions, which are even worse. Not being Hasted in high level combat tends to suck.
I think people underestimate the impact of the extra partial actions for fighter types. Sure, on a full attack, it's a mere extra attack. But the partial action allows fighters to move and still get their full attack, which gives the fighter a much heftier alpha strike, helps when switching targets, and makes it much more difficult to prevent full attacks (and thus damage) through movement.