Here we go again with people whining about transitions in art and concept between editions. Oh, the renewed stench of misplaced nostalgia.
The fact of the matter is that the illustrations in 1ed MM and most other 1ed products (MM II was an exception) were extremely simplistic and almost universally cartoonish. For the most part, they lacked inspiration as well.
Now, on to these two images.
The Balor is okay. Love the head and the horns. The interesting thing here is that the artist actually looked at the image of the Balor in 1ed MM and used that hideous picture as a springboard. That Balor had the same horns and general build. Hell, I think that the weapons are even in the same hands. What I don't like about the Balor is its coloring and the loinclothe. It's an evil spirit... why the Hell is it wearing a loinclothe? The artist (Sam Wood I think, who's usually very good) should have simply surrounded the Balor with flames, thereby hiding the feet, legs, and groin. Problem solved. As far as the coloring, I've always seen Balors in the same light as the Balrogs upon which they're based: Shadows that barely contain the flames of rage and evil that burn within. I would have tried to capture that kind of an image rather than the more "traditional" reddish demon look.
The Marilith is okay. First, to all these people whining about it being emaciated, you're comparing her to a 12 foot tall Demon. Take that into consideration first. Second, she's a DEMON! She's not a beauty queen, and she's not a model. Her appearance maintains the general description from all three D&D editions with an added degree of sensibility. I've never understood why every Marilith looked like some middle-eastern or Indian belly-dancer. Just because the base-model is based upon Kali doesn't mean that they all have long hair, tons of jewels, and are drop dead gorgeous (if you like girls). This image is hideous and otherworldly, precisely what these Demons are.
I will say that I saw that image of the huge Marilith from a recent D&D module and I liked it. However, I thought it was rather lackluster because it looked like virtually every Marilith out there. This one looks like a disgusting Demon with the silhouette of a good looking, slender woman. Her strength to carry those weapons have nothing to do with "natural" strength, but with the strength conferred by her evil and status in The Abyss.
So, can people please back off the nostalgic nonsense. I swear, all it does is limit their ability to consider and explore new things. And makes them look shortsighted and conservative besides.