There was a time when there was only one RPG that you could buy. Arguably, many of us started playing various "monsters" -- goblins, dwarfs, orcs, half-orcs, a 3/4 orc (Don't ask!), thieves, and evil magicians were normal in my gaming groups.
Then came the second RPG -- i.e. Tunnels & Trolls. A new concept (among several) in RPG was introduced - There were no automatic monsters. Every species (or "race," if you prefer) was a "Kindred" and with the same access to legal protection as humans -- provided they lived and interacted with humans.
Yet the dungeons, tunnels, mine shafts, etc., were the haven of so many truly anti-social types of all kindreds. And it wasn't long before the creator of that second RPG wondered what life looked like to those creatures who hid in the dark and hoarded loot the player characters wanted. Gold, jewels, toilet paper, hand sanitizer, and other valuable hoarded objects meant that mostly-human groups would invade these creatures' homes and steal their stuff. Sometimes they killed you, your family, and your little dog too!
So he gave us rules to portray these monsters, giving some of them the chance to defend themselves. Again, a simple, fast rule system -- Khenn was putting his vocational skills as a librarian to work with heavy (pun?) research.
It was GREAT in its first printing, with that great Liz Danforth cover! It was printed again, when Flying Buffalo (FBI) took it back from Metagaming, and we learned how to THINK like monsters, TALK like monsters, EAT like monsters, and occasionally leading a revenge party out of the caves and down on the human villages!
And now - It's even BETTER! An experienced rolegamer will build a character he or she will love, in less than 4 minutes. A new gamer might take a few minutes longer. The adventures and action are from the viewpoint of dragons, huffalumps, demons, and IRS agents (You can build ANY type of character in these rules!) for the first time again! Indeed, Khenn starts out with "How to Think Like a Monster -- and Why Would You?"
It's better - faster - with paper/cardboard/3d printer miniatures, methods to create any new monsters you might dream (a nightmare, I'm sure) up, a Monster Rating Modifiers chart which just happens to list most of the "official" monsters - including empty ratings for a "No Monster" monster, a great adventure that includes a temple to Gristlegrim (I've been looking for one of those for a long time!), and a fully-stocked city! You'll adventure in this setting for a long time...until you get that urge to create your OWN adventure, your OWN city, your OWN world -- and you can control it all! The power! Such POWER!!! BWAHAHA HAHAHA!!
See? You're thinking like a monster already!