Just to recap: The previous two episodes took Marty back to 1931 to break Doc out of jail. He's able to help Doc out, but in the process Marty inadvertently screws up his family's timeline and is almost erased from existence when his grandfather is murdered after giving testimony against a gangster. Though he is able to restore his timeline, he accidently pushes a younger Doc and Edna Strickland closer together.
Back to the Future The Game: Episode 3: Citizen Brown picks up with Marty crashing the DeLorean in an alternate 1986. As a result of Doc and the civic-minded Edna's romance, the two have completely transformed Hill Valley into self-sustaining police state. There's a mandatory uniform, the city is walled off from the outside world and everything is banned.
Of the three episodes released, Citizen Brown is the most complete. The story is great and, unlike the previous two games, there's a bigger issue at stake. Not that Marty disappearing wasn't a big deal, but this story has a heavier weight to it. There's are vibes of both 1984 and THX 1138 running through the story, which I really like.
There's also a more diverse cast, with slightly more complicated storylines, issues and relationships. Marty's parents show up and play a major part in the game as does Jennifer, which is neat.
Puzzles feel more organic to the story than previous episodes. The main form of punishment in Citizen Brown's Hill Valley is demerits. The first section involves Marty trying to do everything he can to earn enough demerits to win an audience with Citizen Brown, which is fun. There are a few story-related ones, though you can also spend time trying to find other ways to earn demerits (there's even a Trophy waiting if you figure them all out).