Full disclosure: I'm a f4nboy, and I have something like 5 PHBs and 2 giftsets on order (for my group and best friend and co-DM -- just call me Santa Claus

). So I have a viewpoint all my own on the issue.
However, I have obtained several of these copies -- and I have a bunch of nitpicks.
My biggest complaint about the new edition is
execution. I am perfectly fine with a lot of things that give others pause: healing surges are a much-needed addition, 'fighters with powers' are okay in my book, and wizards seem a-okay to me.
It feels like another round of playtests with the full docs -- a sort of alpha test period, in which leaks were inevitable and acceptable -- might have helped. The problems I'm complaining about aren't typographical, they're stylistic -- spell descriptions that describe the mechanics of the spell instead of the in-game effects, for instance.
What follows are not problems with the new edition, but complaints about tough decisions that fell the wrong way for me. I can see why they did them, but I don't appreciate the way they went. Other people's MMV, but I suspect if you currently play 3e, they'll bug you too. Hopefully they're not dealbreakers, though, because it's easy to see how there's no right answer here.
There's also a definite feeling of "not enoughness", which will, yes, drive splatbook sales. There aren't enough adventuring items, enough arcane character choice, enough fighter choice, and so on. There's enough to play, and to design mutually different characters {a completely rough guess would be on the order of (8 races) * (8 classes) * (3 or so mechanically interesting builds each -- probably an underestimate, but then not all races appeal to all people) = 180ish characters} but there's still not a wealth of options.
This does mean that splats will be full of awesomely useful stuff -- a good thing, as far as I'm concerned, since I'd have bought them anyway -- but I can
definitely see where it'd be a negative for someone else.
They paradoxically feel too crowded to me.
What's the difference between a Kensai and a Blademaster? In game? Out of game? They just seem to be very mutually toe-steppy. This is important, because the book is so cramped. There are a bunch of maneuvers that get VERY similar descriptions for different effects -- there are only so many ways to hit people, and I suspect game jargon will get used more often.
Upside, it's fairly rich, flavorful jargon -- a reaving strike _means_ something and will conjure the correct imagery, so that's okay.
Strikers, Leaders, Defenders, and Controllers (well, presumably

) have a lot of power effect overlap (themes are different, and usually the actual powers are different too, but you can spot the theme between them fairly easily).
It's not exact, in that the powers are equivalent-but-slightly-different, but it's clear to see that they're analogues.
During design, my guess would be that there were some striker proto powers that got differentiated as they were seeded to roles; the hereditary link is still visible and irks me, because it makes later design nonobvious (I'd rather extend the same power than duplicate the same implementation!) and because it devours up page count.
On the other hand, that page-count makes the book FAR better as a reference manual. When building your character, everything you need about 15th level powers is right there. Mine would make finding what your specific power did fairly complex, so I can see why the actual books spooled it down... ease of book use at the cost of additional content.
I'm also not sure how many power are so overlapped. Healing Word/Inspiring Word, obviously. I just haven't paid enough attention to catch the others, or it's a relatively rare problem. Shrug.