Frankly I thought the old covers were gaudier, especially the smattering of different colored gems on the PHB. At least the new ones stick to a color theme.
I actually gasped aloud in delight at seeing that cover! It looks amazing. Seeing all three books together, you can really see how beautiful a set it is; it meshes together so nicely.
I'd even go so far as to say that, of all WotC 3(.5)e books, the new MM has the best-looking cover.
The 3.5 e books should have their covers be redone as Magic Eye covers... (you know, popular about 7 years ago -- look at it from the right angle and you see a new picture inside; they annoy my brother because he can't see the hidden image )
I like the MM cover, I want to like the DMG cover, I'm just a bit put off by how the title is almost camouflaged within the rest of the design, and I agree the PHB is busy, even a bit gaudy, but it doesn't bother me too much.