If you don't mind the 60s and 70s trend of making school/university movies with a cast of people in their 20s through late 30s attempting to pass as 18-22 yr olds - then you've cleared the first hurdle into appreciating the genius of Jerry Lewis.
The movie itself is entertaining in a way that would not pass muster with anyone born from 1990 on. Visually - its great work for the 60s - but it contains extremely obvious elements that date it such as the extraordinarily vibrant primary colors and even the more subtly things like Stella wearing tights with every outfit in the Professor's fantasy scene (an oddity of conservative opinion in the 60s and 70s was that you could go as short as you liked with skirts, shorts, swimsuits and slits on dresses - as long as the actress wore tights - best example of this being Daisy Duke of course), and of course the thoroughly rampant misogyny. No one really seemed to object to thoroughly inappropriate teacher/student relationships back then - I think you'd be hard pushed to represent this in any movie today.
Jerry Lewis is exceptional but I fear he is lost on current generations who lack the mental maturity to appreciate anything that isn't 99.9% CGI.
The plot is decent - if a little labored (like many of the scenes unfortunately) and there's only so far you can take the Jekyll and Hyde motif - and it's a well directed, well edited and well acted piece of cinema.
I have a personal dislike bordering on hatred of Jazz music - and it heavily underpins this movie - so I find it hard to suffer through these days.
There is some extremely unnecessary unexplained breaking of the fourth wall that while innocuous enough - does kinda have one going "huh?" several times.
All in all, a decent movie - but nothing that was ever gonna gain any plaudits.