Ok, first off I admit that it is a controversial call. He played against Dan Carter and a certain Johnny Wilkinson for years I hear you say. After reading this, you may be more inclined to agree.
Firstly, in the modern game, a game is generally won and lost in the forwards. With a beaten pack, it makes things extremely difficult to win a game of rugby. When the first receiver is automatically on the back foot, and with an onrushing flanker, it can be very hard for an out-half to control a game. Look at any highlight reel, and it won't show up, but the trademark masterstroke of O'Gara down through the years has been his ability to land the ball on a sixpence. No fly-half in world rugby has ever succeeded to punish wingers and fullbacks so devastatingly for being a yard out of position as the Munster man. It is an art-form that he has perfected.
What now must be noted is the 'bottle' of the man; his ability to deliver under maximum pressure. Time and time again we have seen him step back into the pocket when the need was greatest, in both the red of Munster and the green of Ireland, to slot over a winning drop-goal. In 2011, Ireland were on the brink of an embarrassing first ever defeat in Rome, only for O'Gara to come off the bench and hold his nerve to deliver the winning score. Two years earlier, he knocked over that drop-goal in Cardiff to end 61 years of hurt for his country. Or what of the back to back winning drop-goals in a week against Northampton and Castres in 2011? We have seen other great 10s fall at this hurdle. There seems to be an incessant fear of the drop-kick in the southern hemispher game; Carter didn't have the confidence to take it on in the 2007 World Cup against France. But the Corkonian has never shirked the challenge, and won't be forgotten in history for it.
Out-halves have come and gone in the last 13 years. From Spencer to Skrela, Larkham to Lambie, many have faced up against him, but few have stayed the distance. After finally seeing off David Humphreys in their battle for the Ireland jersey, he commandeered Munster to the Promised Land in the Heineken Cup. Having been on three touring Lions squads, he was never picked as the starting fly-half. Perhaps 2001 came too early for him. In 2005, Wilkinson was preferred, living off a reputation built at the World Cup two years previously. The 2009 edition saw a moment that many rugby fans will never forgive ROG for. Stephen Jones was opted for 10, despite the fact that he was outplayed by the Irishman in Cardiff three months previously. O'Gara was thrown straight into the fire in the second test with just 13 minutes left to play and the series at stake. He can't be excused for hitting Fourie Du Preez early to concede the winning penalty, but his over-eagerness to get straight up to speed with the physicality of the game was understandable. However, he did not dwell on this, and got back down to the basics with Munster and Ireland, and fended off the challenge of Sexton for a few years, one of the world's top tens in the prime of career
One thing he has been criticised for is his lack of physicality. But credit where it's due; despite not being the biggest player on the field naturally, he has never shied away from a tackle. It is easy to admire the big runner with the ball, but it takes bigger strength to face up to him knowing you are going to take a hit, but determined to bring him down with you. But with the right protection from his forwards, we have seen how he has controlled a game time and time again.
Now in the twilight of his career, the great man is unlikely to go out with a 6 Nations title, but few would feel too begrudged seeing him have one last hurrah in the Heineken Cup. He never won a World Cup or a Lions Tour, but money can't buy the memories we have of O'Gara in full flow sticking the ball right into the corner on those wet nights in Thomond Park.