I intensely disliked the 4e Players Handbook cover, but I actually liked the cover of the 4e Dungeon Masters Guide. The cover of the 4e Monster Manual is more bad than good in my opinion, both esthetically and "philosophically."
Who the heck is that guy on the cover? Why, Orcus, Demon Prince of the Undead, of course. "But he doesn't look a thing like Orcus!" This is absolutely true, but then Orcus hasn't really looked like himself in a long time. For those with short memories, here's how ol' Goat Boy looked in the 1e Monster Manual (which is itself an almost perfect copy of his previous appearance in Eldritch Wizardry):
Now, I understand and accept that the illustration of even iconic characters will change over time, as each artist interprets the character differently. But, as the 4e MM cover interprets him, I only see the faintest resemblance to the original conception of Orcus. There are some ram's horns, wings, and a skull-tipped wand. Oh yes, and hooves. Kinda. Other than that, though, it looks rather like a different creature to me -- a buffer, more bad ass one. And that's almost certainly the point. The original Orcus illustration has scrawny, satyr-like legs, almost vestigial wings, and a pot belly. What self-respecting adventurer would be afraid of him, right?
But the new re-imagined Orcus is Schwarzenegger with a goat's(?) head. You can tell he's a force to be reckoned with just by looking at him. He's even adopted a body builder pose just to show of us demonic musculature. And he's wearing his WWE championship belt to boot. Oh, and his tail now has spikes all over it now, for some reason or other. Clearly, this is a guy worthy of being the opponent of your player characters, not like that wimp Dave Sutherland drew back in the 70s.
There are a lot of issues here, so I'll start with the differing esthetics. The original Orcus, though a wholly imaginary creation of Gygax (or was it Brian Blume?) looks like a medieval demon. He's a strange concatenation of human and animal parts, some of which look atrophied or distended. He's clearly not natural. In some sense, he might even be called metaphorical, for many of the features of medieval monsters were highly suggestive to the medieval mind of certain qualities that, culturally, they associated with certain referents in the real world. That Orcus' wings are too small to carry his bulk is irrelevant; all that is necessary is that he have wings, for wings equate with flight. The physical plausibility of their operation is utterly beside the point.
Now, I'm not trying to suggest in the slightest that the Sutherland Orcus is a careful product of someone with a deep understanding of the medieval mind, because that'd be laughable. However, the Sutherland drawing, like most of the drawings in the original Monster Manual, is broadly consonant with medieval esthetics. Or perhaps I should say that it calls them to mind. There's something weirdly primal about that goofy Orcus DCS drew. I've always found medieval demonic images to be far creepier than modern ones, precisely because they have some atavistic connection to aspects of my cultural memory. Modern demons are just imaginary creatures; they're not monsters, if you catch my meaning. Wayne Reynolds' Orcus isn't a demon. Look at how muscular and physically powerful he is. That's a creature that inspires fear for my life, whereas Sutherland's Orcus is one that inspires fear for my soul.
I'm just going to ignore the fact that this piece is another strike-a-pose piece from the latter day Elmore school, even if it is far more dynamic than most Elmore pieces. Of course, "dynamic" is a relative term, since it's not clear from context that Orcus is actually doing anything other than flexing his muscles for the judges. Take a good look at his wand, though, and compare it to the one in the Sutherland illo. The Reynolds version looks as if it's an actual skull (plus some vertebrae) mounted onto a black metallic handle. The DCS version is just a skull, possibly even just a carved one, atop a black wand. What are the odds that 4e has introduced a backstory to Orcus' wand? I'll bet you the the identity of the skull's original "owner" is made clear (or will be before long). A god whom Orcus slew perhaps? Or some powerful being Orcus defeated in his ancient climb to demonic princedom? Maybe I'm being unfair, but the new version of his wand just begs for explanation and brandification. It's not merely a symbolic representation of Orcus' affinity with the power of death; it's instead a trademarkable image that helps build IP.
There's also the potentially bigger issue that says a great deal about the design philosophy of 4e. By picking a single (yes, he has a couple of henchmen with him, I know), powerful opponent for the cover of the Monster Manual rather than illustrating several, I can't help but think that this is what's deemed the ideal 4e encounter -- the set piece against a "boss" monster (known as "solo" monsters in 4e). I know it's unfashionable to make comparisons between 4e and video games, but so be it. The reality is that there's clearly been a shift toward a "cinematic" model for combat in 4e, treating them as big special effects extravaganzas, where the player characters get to show off how cool and powerful they are. The placing of Orcus on the cover of the MM is WotC's way of saying, "Isn't this the kind of bad guy whose ass you want to kick?" There's nothing wrong with that, if that's what the average D&D player actually wants out of the game, but I hope I can be forgiven in saying that that's a huge shift away from the philosophy and esthetics of OD&D, never mind the pulp fantasy literature that inspired it.
The cover of the Monster Manual pretty well cemented my dislike for 4e. I disliked the contents already for various reasons, but the cover was the icing on the cake. The fetishization of the D&D's most powerful entities has always sat poorly with me, but 4e's cover takes it to new heights. It's a reductionist mentality that treats even the Demon Prince of the Undead as another notch on your character's belt as he claws his way toward immortality. Indeed, it's a wholesale rejection of the Gygaxian "naturalist" approach to fantasy roleplaying. I hesitate to call this the worst MM cover ever, given how poor its competitors are, but I will say that this is the first cover whose philosophical underpinnings are so reprehensible to me that it actually makes the cover of the 1e version look inspired by comparison. That takes a singular kind of badness. Bravo.