But then if you have more than an attack per round, and use greater feint, what prevents you from doing a feint attack before the 1st attack, and one before the 2nd attack, and so on?
That's what the rule says, one feint per round per viable opponent. What you can do though is when you finish a round with no more attacks to make, you can feint someone you haven't feinted that round as a free action as your last action that round, then next round the feinted character will be prone to a sneak attack. If he survives that sneak attack on that second round, you can feint him again, because you haven't feinted him that round.
Feint isn´t that powerfull as it was before, the BAB bonus to sense motive makes it quite dificult to pull out on a regular basis.
Yeah, that's pretty hard to beat. Nonetheless, there are some new rules in the Hyboria's series that can work to overcome that. Take for instanse the multiclassing variant rules for the Ruffian (thief-barbarian) from Hyboria's fallen, he can take Waiting for the Chance in lieu of the thief's trap sense +3 as long as he has 4 levels in barbarian. Then he can spend a full round in total defense, and the next round he can add his own BAB to his feint check, that levels things a bit. There is also the Read an Opponent rule for soldiers from Hyboria's Finest. You can make a sense motive check, modified by your BAB, vs a DC of 10+opponents level, for every 5 points you exceed the DC, you gain a +1 to either one of: attack rolls, DV, saving thorws or skill checks, which could be added to your bluff check to feint. If you consider that there is a new thief special ability that allows you to take 20 on any sense motive check you make, you could be getting a very good bonus to feint if you combine all those abilities.
I would really like to understand why TR and HF Gfeint are diferent... and i expect HF Gfeint is the revised one (i didn´t like TR´s one)
It seems they rised the prerequisites and made the feat more useful. Before, feinting as a move action vs evryone you threatened, left you able to deliver a single attack on that round, and if you were surrounded, that kind of sucked, they could get you before you could deliver the rest of your sneak attacks. Then, I don't quite like abilities where you make a single check vs several targets, that means if you rolled low, you could fail against evryone. The new feat overcomes these inconveniences.