I really dislike this feat. It allows any creature with greater reach than its opponent to pretty much automatically win.
For example take an ogre vs a human fighter with a non-reach weapon. As the fighter closes the ogre takes an aoo - lets say it does 10 damage, and that the ogre and the human are equally strong (even this is unlikely). The fighter must then beat the ogre by 6 points in an opposed roll, or be pushed back. On the ogre's turn it takes a full attack, then 5' steps back. Repeat.
The fighter must make an extremely difficult roll (in most cases I suspect the difference would be far greater than 6 - larger creatures tend to be very strong and deal lots of damage on the aoo) or be kept away indefinitely, while the ogre gets a full attack AND an aoo each round. Throw combat reflexes into the fray and the ogre can potentially hold off multiple opponents..
Now I appreciate that the fighter may have other options such as ranged attacks, but if he's specialised for melee (as many fighters are) then this will negate a great deal of his class abilities (also his melee weapon will likely be far more powerful magically than his ranged weapon).
Compared to say, Weapon Focus, or even better Spell Focus, which was apparently seen as too powerful, this seems to me way over the top.