If you loved Back to the Future, try Phineas and Ferb The Movie: Across the 2nd Dimension
A bridge between a film you've already seen and one most people haven't. Phineas and Ferb The Movie: Across the 2nd Dimension has roughly 36.3× fewer votes than Back to the Future — it's a deeper cut, not a mainstream recommendation. Here's what they share, and what the second one does that the first one doesn't.

Back to the Future

Phineas and Ferb The Movie: Across the 2nd Dimension
What they share
Theyboth carry the playful mood tag, and they sit in Adventure / Comedy / Science Fiction territory. If that's the register that drew you to Back to the Future, the second film will land in a comparable space — through a different lens.
What Phineas and Ferb The Movie: Across the 2nd Dimension is
The multiverse: still having its moment. Phineas and Ferb travel to a parallel dimension where Doofenshmirtz is in charge, which is bad news for everyone. Luckily, Perry the Platypus is also on hand, living a double life as a secret agent. A solid afternoon's work.