The Reds’ stunning ascent up the second-tier standings under the Frenchman saw them go from 21st place when he arrived in October to the top-six by early March.
Having broken into the play-off places following a run of seven consecutive victories, the Oakwell club have never looked in any danger of slipping out of them again, eventually wrapping up fifth spot by holding champions Norwich City to a 2-2 draw on the final day of 2020-21.
And, when considering his players' achievements this term, Ismael pointed to the way that the Reds coped with the transition from chasers to a team with so much to lose as a big positive.
"The big example for me is since we got into a play-off spot, we never dropped down [below sixth] and it shows the mentality of the guys," he said.
"From a chasing position to being chased is a big difference in our approach to the games.
"To keep the pressure away from us, it was a great performance."
Barnsley now face a two-legged semi-final showdown with Swansea City, a side who completed a league double over them during the regular season.
But Ismael has dismissed the relevance of those results and insists that his team are now a different animal to the one that was beaten 2-0 both home and away by the Swans.
"We are very proud of the guys for the season, but now the Championship is finished, it’s time to recover and to prepare for the new competition," the former Bayern Munich defender added.
"It [losing both league games to City] doesn't matter now. If you can remember at that time, we played Swansea twice in the space of a short time, four weeks between December and January and we were a completely different team.
"Swansea at that time were really strong, but now the momentum has changed and the momentum is more on our side. We have Daryl Dike, we have Carlton Morris, we have more options and the desire now is to change the story of this season against Swansea.
"It will be a fight. We know that Swansea change their way to play football, they adapt, but we have enough time to speak about Swansea, to prepare for the first leg."