Finally I got to make a quick trip to the FLGS to check the PHB and MM out... I couldn't really browse all of the MM

but I checked out some of my favourite sections: Dragons, Giants, Angels & Demons & Devils, Orcs, Trolls, Ogres, Genies...
Overall I think it's a really good book, better than the 3e MM. My first (non in-depth) opinion in a nutshell:
PROS
- much more readable than 3e-era monster manuals, thanks to generally shorter information and better layout
- fluff information seemed very inspiring to me, although it could have been much more
- artwork
quality significantly better than 3e, although not a 100% score, there are still several ugly pictures (for example the oozes)
- artwork
concepts (or changes to previous editions) match my taste in most cases I've checked (for example, I liked the new take on orcs and trolls, not so much the overly muscular angels)
- every monster has a picture
- there are a very few omissions of classic monsters, and many additions I like, for example more dragons, demons and genies than in 3e
CONS
- really not much information on each monster:
(1) crunch is much less than 3e, but while this in general is a GOOD feature (that 5e doesn't
need the same amount of data), there seemed to be a lot monsters which look just like a small bag of hp with no special abilities
(2) fluff is of good quality, but could have been more at least for
some monsters, while it seems they standardized every monster to exactly 3 paragraphs of fluff, 3-4 lines each
- some artwork is indeed unnecessarily too large, as if they preferred padding the space by enlarging the pictures to avoid putting more information
- almost total lack of templates
As for the art, it does take up a lot of space, but it also saves space because they don't have to devote a paragraph to describing what the creature looks like.
This is true. I don't miss the written physical descriptions when every monster has a picture.