I like them, but I don't feel that they do enough to incorporate the skills of the opposing character. ON the surface, there is trip, sunder, grapple, bullrush, disarm and overrun.
What I did was add an opposing skill that can be added to the cmb of the opponent to determine the DC of the attack.
For instance, grapple has an opposing skill of escape artist. escape artist is added to the CMB score to determine the DC. The other abilities use athletics as an opposing skill.
Also for grapple, I took a note from the other combat maneuvers and determinded degrees of grapple depending on how well the dc is beat.
None of these abilities receive an "attack of opportunity" instead dependong how awful a player loses he receives negative reactionary results.
For example this is the reactionary result for a failed grapple.
Reactionary Results: 0 = 1/2 standard attack damage to opponent
-10 = full damage
AGain, the idea is to reduce the number of rolls in combat and always keep the focus of rolling on the players turn .