What is this film about?

It's a love-letter to Chicago, disguised as a road picture. In this case, Dan and John on an almost continuous journey around more Chicago locales than you can count on all of your available digits.

It's a musical. Throughout the "road trip", the film exploits every opportunity to enlist so many musical legends (who find reasons to "break out in song"), that you probably won't be able to keep track of all of them, either.

It's an excuse to throw in a long list of famous comedians, and other celebrities, strewn throughout the movie in bit parts, just for grins. (You should pay attention to almost every character that shows up along the journey, as virtually all of them are someone famous, e.g. even Twiggy shows up at one point.)

It's an excuse to destroy, in unimaginably creative ways, an entire mall, and numerous other buildings, as a result of chases, vendettas, etc., just in case you need an "action fix" to "round out" the movie's musical and comedic experience. (A decent percentage of those destructive activities, perpetrated by Carrie Fisher's character.)

There is a "plot thread" that provides an underlying reason for Dan and John's journey, but it's just there to facilitate all of the craziness. The journey is never boring (there's never time to get bored), and it is an awful lot of fun.

I finally decided to review this, while watching the 2020 4K UHD release (which, as an aside, looks great). I would be remiss not to mention that it's a bit hard to watch the film, and not feel a hint of sadness, based upon the fact that 40 years on, from its original release, so many of the actors, musicians, and comedians it features, are simply not with us anymore. For some, that is simply a consequence of age, but there are far too many others that should have still been with us. The only silver lining is that we get to see why we enjoyed them, while we had them.

I highly recommend this. It successfully melds so many film genres together into a single film, that it's almost impossible not to have fun.