The demo took me about an hour to beat and features a self-contained, special chapter which is not a part of the main story, so playing through this won't spoil stuff (outside of being initially introduced to the new cast of characters, and some of the new game mechanics) for anyone who's looking to avoid plot details.
If there are any returning fans of the series that think they don't need any convincing, you might still wanna play through this since you'll be given "a special reward" in the full game if you import your save file from the demo.
Also, just a heads up for any PC players: The game has a configuration tool which you'll only see if you launch the game from your Library on Steam. You won't see it if you use a desktop shortcut, for example.
The tool will allow you to adjust some very basic graphics settings, and also what kind of control prompts you'll see in-game. The ones for an Xbox controller are on by default, so if you're planning on playing on mouse & keyboard, you'll have to change it there first. Finally, F3 brings up a list of inputs once you're in the game, but it won't work until you've gained control of your character.