In three seasons with Munster, as the province's head coach, Australian-born Gaffney took them to back-to-back Heineken Cup semi-finals in 2003 and 2004.
"Alan is a very good coach, he has been around the game for a very long time and there are not many around who know the game as well as him," said O'Driscoll.
"He certainly changed the mindset here in Munster when he arrived in 2002. Perhaps things had been pretty similar for a number of seasons and he certainly brought a fresh approach and a lot of new ideas.
"No doubt about it, he helped us develop into a better team during his time with Munster."
Munster, the 2006 Heineken Cup champions and finalists in both 2000 and 2002, are in the knock-out stages mix for a record 10th successive season and beat Saracens by single point margins when they were in the same pool in the 1999/2000 season.
"I played against Saracens in the pre-season friendly we had with them at Musgrave Park last year so I know that they are a very good team," O'Driscoll added.
"Of course we were without our World Cup players and they were minus a few of their own but they are without a doubt an excellent side with a number of big game players. They will be formidable opposition.
"Any team that reaches the Heineken Cup semi-finals has to be a top side and we rate Saracens as being right up there.
"A Heineken Cup semi-final is just a massive game - and everyone knows this tournament means such a huge amount to us - but, while we want to go on and win it again, all we are concentrating on at the moment is the Saracens challenge.
"In their quarter-final win over the Ospreys they took their chances and proved very strong in all aspects of play and, any side who can turn the Ospreys over, has certainly proved their worth," the Corkman insisted.
"We do know the Ricoh Arena as we played London Wasps there in our opening Pool 5 match this season - and lost by a point. But the stadium is great and as it is quite a big soccer pitch it should make for a good game."