Giovanni Trapattoni's side lost all three of their Group C games with their final defeat coming in a 2-0 capitulation to Italy, who progressed into the quarter-final stage alongside Spain.
Keane also admits Ireland were never going to adapt their style of play in the run-up to Euro 2012 because their original mentality ensured their place at the tournament.
"We have no excuses, our preparations went fine and we can stand here all night and discuss but we couldn't be prepared better," Keane said.
"The criticism is always there, was for last four years, and we have always been playing that way, got our results, got here, so why change in the tournament? It's managers decision but we were quite happy the way we played for four years.
"We are obviously disappointed, we wanted to give something to our fans and to ourselves to go home with and as we didn't, we are not happy. We played well, it was a different game to the way we played previously but then come up two set pieces from which we concede and we know that it should be our stronger side. "
Keane insists the Ireland squad were fully committed in their three matches but concedes the better sides progressed from the group stage.
"After all we got beaten three times but there can't be any complains to the players, we all gave our one hundred percent, we can put our hand high and simply say that we were beaten by better boys," said Keane.
"Of course, you come to this tournament with an aim to win, being so many years in football, being competitive, professional, you never think you will end up on the back foot.
"Tonight, we got in their faces, played better from the start but we haven't created much chances for ourselves and then got beaten from a corner from the smaller man on the pitch so that is hugely disappointing."