How to Unlock Diablo III Cinematics without Finishing the Game

All you have to do is edit the config file D3Prefs.txt. It is not found in the installation directory of the game, but rather in My Documents/Diablo III folder. There is always your computer’s search function if you cannot find it manually.

Once opened, you’ll see a lot of settings. We only need to edit four lines among them:

PlayedCutscene0 "15"

PlayedCutscene1 "15"

PlayedCutscene2 "23"

PlayedCutscene3 "143"

The numbers enclosed by double-quotation marks in your config file may not be the same as the numbers above.To be able to view all cinematics, regardless of game completion, all you have to do is match those numbers.

The PlayedCutscene0 stands for Act I cinematics, PlayedCutscene1 for those in Act II, and so forth. Don’t bother asking me what the numbers stand for. I don’t have any idea myself. Just match it!

Note that the cinematics have only been unlocked to the computer you’re currently using. It does not bind to your account. Chances are when you run Diablo III in another computer, you will need to modify the numbers in the config file (or finish the game) again to unlock the cinematics.

Source