Having been crushed in the opening Test in Auckland, the tourists levelled in Wellington, only for the return match at Eden Park to end 15-15 and result in a drawn series.
Ireland flanker O'Brien played in all three Tests and believes it was a missed opportunity for a rare series win in the Land of the Long White Cloud.
When quizzed on the reasons why his team did not succeed overall, the Leinster star was extremely frank in his assessment, levelling the blame firmly at Warren Gatland and his coaching staff for their methods in the build-up to the first and third matches.
"To be honest, I'd be pretty critical of it because I think we should have won the tour and we probably should have won it comfortably," O'Brien said in an interview with Newstalk.
"There's the best players in the world on a Lions tour. I know you are playing the best team in the world but with the quality and strength in depth we had, we probably should have won the tour.
"It wasn't down to fatigue. It was probably management a bit, in terms of how our weeks went.
"The first week, we definitely over-trained on the Thursday and maybe the coaches were panicking a little bit about getting the information into us. On the first week [of the first Test], we had a triple [session] day, [the] lads' legs were heavy on the Thursday and we were playing the All Blacks on Saturday.
"There was probably no need for that but it's just the way it was managed. We had said it, at the time, and they pulled back a bit."