Todd Russell’s review published on Letterboxd:
Marty and Doc Brown are back for another adventure, this time traveling into the future to try and prevent something bad from happening to Marty's son. Crispin Glover does not return as Marty's dad, and they tried to make a doppelganger with a different actor, but it's clear he's missing from the cast, even if it was just a very small part.
This one has a darker, bleaker feel in that an alternate future is created by Marty making a momentary lapse of judgment seeking to possibly use the time machine for financial gain. Biff The Bully Tannen (Thomas F. Wilson reprising his role) overhears Marty and steals his idea. How Biff becomes knowledgeable enough to use the time machine is one of several gaffs.
An interesting sidenote: this was filmed at the same time as Back to the Future Part III and you'll see some of part III foreshadowed in this one.
This one isn't as tight and logical as the first one, but it's still fun. Enough of the original was kept in tact to keep me entertained, but it exists to its detriment in the shadow of the first. Sequels are a tough business. Recommended.