Dungeons & Dragons: Chronicles of Mystara

This is a pretty good Arcade Beat-em-up, with lots of branching paths and levels.
There's also a good amount of characters to pick from too, and they all are surprisingly unique too.

Chronicles of Mystaria is a sequel to Tower of Doom.
You get both games from that Steam link, and both are based on DnD 2nd edition.
The characters and monsters all follow the same rules from the tabletop game, which is fun.

Playing online with randoms can be annoying as a lot of them are Experts/Powergamers that expect you to do certain things.

One of the best beat-em-ups ever made, with tons of secrets and neat stuff. Has branching paths and optional areas, too.
An interesting note is that it was actually written up as a traditional tabletop campaign as part of the development process.