"Where someone would assume that this guy was going for a ruck and that was his main mantra - don't effin' assume!
"He was very good. He developed a lot of guys, he did different coaching techniques to other coaches. He did a lot of work on videos with guys, a lot of analysis.
"He'd have the opposition team very well sussed. It would be up to the team then to go out and execute. Sometimes we did that and we had great days under him and sometimes we didn't do it.
"He just has a very, very clever rugby brain. I think he improved a lot of guys during his time here," added the Limerick man.
With Gaffney's inside knowledge of the Munster squad, O'Connell and company have been working their way through the video vaults with former out-half Jason Holland, now the province's video analyst, picking holes in Sarries' game.
"We looked at their game against Wasps last weekend and you'll find the tries they conceded and which effectively cost them the game won't happen on Sunday. Alan will guarantee that.
"And if you look at the five tries they scored against probably one of the best defences in the Guinness Premiership, you'll see that they had a lot of the hallmarks of Alan's play - guys flat on the line, very quick ball, offloading and so on," O'Connell explained.
"It's going to be a massive factor even though we've changed since Alan was here. Okay, a lot of the same guys are still here but now we're much more experienced.
"There have been some good experiences and some bad experiences but I think the bad experiences make you better."
Experience could be a key factor on Sunday as Munster contest their seventh Heineken Cup semi-final, whereas Saracens have never reached this stage before.
O'Connell is quietly confident that his side, boasting streetwise European campaigners like Ronan O'Gara and Alan Quinlan, can beat Saracens and that their greater experience will help them overwhelm Gaffney's men.
"I think experience is vital. When you're young you think nothing of experience, you think it's just a word.
"But I think it's very important in terms of playing cup rugby. In terms of trying to win the game, not trying to win it early on, taking your time to win it and making sure you get your basics right.
"That's the important thing about cup rugby. A lot of us would have grown up playing cup rugby, between schools and a bit of senior cup," he said.
"Anthony (Foley) would have had a great influence over a lot of us who are playing cup rugby. Deccie (Declan Kidney) played it and coached it. These things are very important for a squad at this stage of the competition."