Well, I shoudn't do that. You should save all the 300 and find it out by yourself
But that's ok, I'll tell you.
After shutting down Soulstorm Brewery, you get that good ending movie you mentioned above.
Right after the movie, a couple of screens appear with congratulations stuff for saving all he 300 mudokons, and a few lines about Abe's mother (nothing new nowadays, but back to 1998, it was big spoilers!).
Then you watch another movie, but it's more like a slide show, with production pictures of Abe's Exoddus, many of them are already available now, in the web.
But I think the biggest bonus is to know that you made it. You hacked every singled screen of the entire game, and saved every single mudokon that was possible to save.
I hope Munch's Oddysee keep this "secret areas" concept, so that we can look behind every stone, avery tree, every wall, searching the next hidden area, full of desperate modokon slaves to be rescued.