One of the least mentally challenging films has to be 'The Rocker'.
Good fun about a comeback drummer who plays with his nephews band.
The other I like, again not particularly challenging (says something about my film choices) 'Rockstar'
about a lad who gets up from the audience to carry on when the lead singer leaves the band.
I have to admit to liking cheesy 50's and 60's musicals like Summer Holiday
And I agree with Alparrott that The Committments
is an excellent flm