No, it's not Day of the Tentacle. Sorry. But it's something almost as neat: a playthrough of Jordan Mechner's The Last Express, re-cut to look like an animated film.
Poor Last Express was a PC adventure game from the 90's, which nobody really played because the publisher's marketing team didn't market it. At all. Though it didn't help that it was an art nouveau murder mystery adventure game set on a train in 1914.
But it looked amazing, which I guess is why we're here. The game featured a gorgeous, hand-drawn art style, rotoscoped from real actors (much like Mechner's Prince of Persia was), and this clip (captured by Mechner himself) shows just how many of these sequences were in the game because this "cartoon" - covering the entire game's plot - runs for a whopping 75 minutes.
Might want to fix yourself a cup of tea before you settle in.