The Scot has overseen a major overhaul of the first-team squad since taking over as manager at Villa Park in June 2012.
Lambert guided Villa to 15th in the Premier League table in his first season in charge after putting his faith in youth.
Villa have been inconsistent thus far in the current campaign, and although Lambert's side occupy 12th spot in the table they are only four points better off than third-bottom Sunderland.
Weimann believes Villa have made great strides under Lambert and hailed the the former Scotland midfielder's man-management skills.
"He's brilliant to work with. He's doing an unbelievable job when you look at it," Weimann told the club's official website.
"He's completely changed the team. From when he arrived, he's transformed the look of the squad.
"That's not easy doing that, being competitive and winning football matches but he has managed that superbly.
"We're now sitting 12th in the table in his second season in charge. I know it's very tight but we feel positive about our position and the remaining weeks to come. We have progressed as a group, definitely.
"He's very hands-on and approachable with his players. If you have done something good, he will let you know immediately and praise you. Equally, he will get his message across to you if you're not doing things how he wants or he thinks you can improve.
"His man-management skills are excellent. He will always tell you clearly what he thinks."
Weimann has featured prominently this season, making 25 appearances in the Premier League and scoring three goals.
