This one was cute. That's probably not the reaction they were going for, but hey, I wasn't the one who chose the art. I'm not in a place where I can post photos, so I'll just have to try and describe it in a way that doesn't make me sound like a total dick.
If you were to make a movie about a sad, but creative teenager, who made up for their lack of popularity by having a rich inner life, and you wanted to show that your main character wasn't really an artist, but they did have an active imagination, you would probably direct the professionals in your art department to create something that looked exactly like the cover of the AD&D 1st edition Monster Manual.
Which is to say, if I saw something that looked like that today, I'd assume it was a professional doing an impression of an amateur. In 1979? Maybe it's the most expensive professional TSR can afford, having no contacts in the underground comics scene and only an rpg-company's budget. It's probably at least another decade before they can afford those Frazetta-inspired watercolors that I've come to associate with "D&D art."
Aside from the art, it's serviceable. It suffers from comparison to its 2nd Edition follow up, which is probably the greatest fantasy bestiary ever printed, but it delivers what it promises - plenty of monsters to use in your campaign, from the iconic (dragons, orcs, giant spiders) to the thinly-veiled pop-culture references (don't think I didn't notice that flesh golems are just one long riff on Frankenstein) to the needlessly bizarre (so, a "Thought Eater" is basically a psychically-endowed platypus skeleton that floats around in a nearby alternate dimension and steals magic spells . . ?). In other words, it set a tone early, and D&D has stuck with it for more than 40 years. I can respect that.
The only complaint I have, and this is going to sound churlish because it's fundamental to the very concept of an rpg monster book, is that AD&D monsters are kind of . . .poorly executed. I'm not talking about anything on the fiction layer here, just their mechanical implementation.
The upside is that they've got very simple and easy to use stat blocks. But the reason these blocks are so easy to use is that they all describe basically the same encounter - whittle away at this sack of hit points while avoiding these mechanically interchangeable attacks. The only thing that varies is the numbers.
Sort of. There are also special abilities, which are usually just spells from the players handbook (or inexplicable instant-death effects, like the bite of a poisonous snake), and occasional descriptions of battle tactics, which only have teeth if the DM decides to give it to them. Of course, it's probably no worse than the opposite extreme - in a game like Exalted where every serious enemy is exactly as complicated as a fully-developed player character.
It's a hard act to balance, and not a task I envy, but I can't ignore that in our time, this is basically a solved problem - D&D 4th Edition's encounter-balanced monsters are pretty much the gold standard for rpg enemy design. Here, in AD&D world, when creatures get powers at all, they're pretty much on a daily recharge, and I can't help wondering - who is this for? Who is tracking this monster's entire day?
You know what, though, that complaint is basically nothing. Most rpg monsters are poorly executed. These were no worse than average and better than some. So overall, I'd have to call the AD&D Monster Manual a good book. Not just on the curve for older games, but in general. There's a lot to discover in its pages, and it is only slightly annoying that it mentions an Ogre Magi from Japan, a Rakshasa from India, and a Portuguese Man of War.
UKSS Contribution: This is kind of a target-rich environment here. The thing where you could subdue Dragons was included here, so that could almost carry over, but I figure a new book merits a new bit of canon.
I'm going to go with the Giant Lynx. There are a lot of giant versions of normal animals in this book, but only the Lynx could speak the common tongue and only the Lynx got a cheesy little comic where cute, cartoon adventurers expressed their shock and disbelief at this fact.