My dislike for the art direction and marketing of AD&D Second Edition is well established, but the truth of the matter is that I played and indeed enjoyed 2e without too much complaint in the early years of its existence. By and large, the rules of 2e are not so far removed from those of 1e that they've wandered too far off the campus of the old school. The presentation, content, and marketing of 2e are another matter entirely, as its "Monster Manual" reveals:
The first thing you'll notice is that the 2e version of this "book" carries a different name, the Monstrous Compendium. I put "book" in scare quotes, because the MC was not in fact a book at all, but rather a D-Ring binder decorated with Jeff Easley art and TSR promotional text. The pages of the MC were loose-leaf sheets with three holes along on side to be place in the binder. The theory was that the DM could simply remove the sheets he needed for play and leave the rest of the binder elsewhere, without the need for flipping through a large book. In addition, as future volumes of the MC were released -- see that "Volume One" on the cover? -- you could just interpolate the new sheet with those of other other as you wish, in the process creating a custom volume that included only those monsters the DM used in his adventures or campaign.
Unfortunately, very few monsters occupied more than one side of a sheet, which made a mockery of any attempt to alphabetize a large collection of them. The same problem occurred when you attempted to weed out monsters you didn't like or didn't need to use, as there was a good chance that at least some of them had useful information on monsters you did use on their reverse. TSR attempted to correct this flaw primarily by padding out the entries for many monsters, adding levels of detail that were frankly unnecessary and weakened the game's tool kit credentials by establishing all sorts of "facts" about orcs or dragons we'd never heard of before.
The cover art of the binder itself isn't terrible, at least in general concept. I'm not happy with the execution, which is much more cartoony than the covers of the other two 2e volumes. The piece also does not depict a scene, but is it a "strike a pose" illustration, with three monsters standing together for no good reason and without any context. TSR seems to have realized that iconic D&D monsters -- in this case the beholder, umber hulk, and displacer beast -- are iconic for a reason. I have mixed feelings about this. On the one hand, I am glad they're paying homage to certain distinctive elements of the game. On the other hand, it's pretty clear that TSR sees these distinctive elements as trademarkable images they can use to promote the D&D "brand." Unsurprisingly, that makes me a little unhappy.
Equally unsurprisingly, TSR learned from its mistakes and four years later released the Monstrous Manual (again, note the name change) that collected together many creatures from the Monstrous Compendium volumes in a single hardcover, complete with full-color illustrations. Interestingly, the Monstrous Manual entries were all confined to a single page in most cases, just as if they'd be sheets in the abandoned MC.
The cover to this book is again by Jeff Easley and follows a similar style to that of the Monstrous Compendium's first volume. However, the monsters are (mostly) different. The beholder is still there, which is not surprisingly given how 2e era TSR treated the monster as the quasi-mascot of the game. We also see a red dragon, which I think is appropriate. Joining them are a lich, a minotaur, and a thri-kreen. The thri-kreen is an interesting choice and I suspect it was there in order to make a connection to the Dark Sun campaign setting, although it may just be that the race was a popular one. All in all, it's not a terribly strong piece, but it's not wretched. My main beef with it is that it simply makes no sense as anything other than a cover. It looks like a movie poster or promotional shot from a TV series rather than an illustration with any coherence of its own.
And that, right there, is my biggest problem with both these covers and with 2e generally: incoherence. The rules of 2e are still (mostly) the same Gygaxian chassis but 2e adds a new body, paint job, and tail fins that suggest the people in charge of marketing and promoting D&D either didn't understand its foundations or hoped to move away from them. I suspect it's a little bit of both. 2e is part of a major push by TSR to ride the mass media success of fantasy, which is why we got so many divergent settings for D&D; this was the first edition that was influenced by its popular culture brainchildren rather than being an engine of influence in its own right. If, as I have argued, Dragonlance is where D&D first made the acquaintance of Mephistopheles, 2e is where the game signed on the dotted line in its own blood.