Attribute/Stat Based (STR, CON, PER, etc) Class Based (Pilot, Wizard, Scientist, etc) Dice (Various) Level Based (Earn XP and level up) Race Based (Player Race/Species affects gameplay) Random Attribute Generation (during Character Creation)
It's very reassuring to read an old AD&D supplement and see how well this game stood the test of time. Even flipping through «Monstrous Compendium: Volume One» one can realize how far back the roots of many iconic monsters from Dungeons & Dragons can go. Granted, many of the entries from this book are simply too bizarre to roam about in a dungeon form nowadays, but most os the information presented here can — and will — generate great adversaries or NPCs for games of any edition, even fourth.
The only downside of the "book" (actually a binder), as I see it, is the fact it's... well, a binder. This was all well and good for the way TSR used to print out those Monstrous Supplements, but flipping through this (specially my copy, which's made out of volumes 1 and 2) is a pain.
If you're a fan of old-times D&D or miss the look and feel of TSR, you should treat yourself with a copy of this book if you find yourself in the position of buying one.