Sherwood was appointed as Paul Lambert's successor in February after the former Scotland midfielder paid the price for a run of 10 Premier League games without a win.
Villa were in the relegation zone when Sherwood took charge, but are now three points clear of third-bottom Burnley and captain Vlaar has been impressed with the impact made by the ex-Tottenham head coach.
He told the club's official website: "I haven't had too many sessions with the gaffer - and only one game.
"But I know there's a big difference now at Bodymoor Heath and at Villa Park. There's a lot more energy and positive vibes going through the building.
"You feel it everywhere and that's a good thing. You can see it with the players and all of the people who work at the club.
"I think having a laugh and a joke is good and he's the type of manager who likes to do that with his players.
"The stress levels, even with the situation that we're in, are lower than before which makes it easier for everyone to work in this environment.
"To me, that's important. Now we need to go on and get some more results.
"We've had some good results already and were unlucky in our last game against Swansea.
"We've scored more goals and are creating more so I'm really pleased."
Villa face a difficult trip to Manchester United when the Premier League resumes on Saturday following the international break.
