the second edition monster Manual is a great example of what A monster Manual should be. it gives you not only the hard core mechanics of the monsters, but has sections on ecology and behavior. both great pieces of fluff that are missing from many modern monster sections. this fluff allows you to play the monster and make it more than just a for in the PC’s path.
this monster manual replaces the monstrous compendiums vol 1 and 2 that came before it. these compendiums were loose leaf and had holes punched so you could put them in a binder. the idea behind that was you could take out and only carry the monsters you need. it was also designed to allow easy insertion of new monster sheets. unfortunately neither option worked out as well as they wanted to do. by taking out the pages repeatedly it caused to holes to rip and made the paper harder to store and the formatting of the monsters sometimes made putting them in true alphabetical order impossible. therefore the monster manual was reborn. it was a sturdy book with all the monsters you would need for every level of game play.
the art work for the monsters were good for their time and age. my favorite is the invisible stalker, the art work for it was beyond great it was the best art work ever in any monster manual bar none.
I think that you can clearly see that the invisible stalkers art is indeed the best. not like the modern depictions that make it visible. the art work is so great even Mathew mercer of critical role likes it.
Obviously if you are going to play 2e AD&D you will need this book and it does not seem like a pointless purchase as it has great art work and is a fun read with all of the fluff in it.