The Blues Brothers is hands down one of the most entertaining films ever. John Belushi and Dan Aykroyd are absolutely hilarious, the sheer number of entertainers is amazing (where else can you get the likes of James Brown, Aretha Franklin, Ray Charles and Cab Calloway in one film?), the acting cast is equally impressive, and the absurdity of the plot and everyone's acceptance of the goings-on, are what make it so great. The brothers "are on a Mission from God" (and causing complete and total mayhem on the way) to pay taxes on a building owned by the church, which would be exempt from taxes to begin with!!
