Huh! I am just absolutely entranced by the PHB2. I think it's the best supplement to date... Here are my own thoughts...
(1) The new races. I love Devas. Lovelovelove them. I think they have a wonderful flavor, and they can really shine with a few feats. They do make pretty excellent clerics, since they get a Wisdom bonus. They make outstanding Invokers, too. They don't make great Paladins, which I'm fine with - Devas are
different than Aasimar, now. They're not just reskinned & renamed.
I think the Gnome seems pretty good, though I still don't know how many we'll see. I expect to see a few feylocks, and a few bards, and maybe a wizard or two... but they're about as useful to me as they were before.
Goliaths are fine. They do nothing for me, but a Str/Con race isn't nearly as overpowering in 4e as it was in 3e. I think they'll make great Barbarians and Wardens, but I don't know if they're the best choice for anything else. Although Str/Con seems great for a fighter, I don't think their feat selection encourages this.
Half-Orcs are pretty cool. I'd rather they were Str/Wis, but I like that they make excellent brutal & rattling rogues now. Their class flavor is geared towards barbarians, and I think, much like Tieflings and Infernal Warlocks, with a few feats they'll work out great.
Shifters have never, ever done anything for me. I didn't care for them in Eberron, and I don't love them now. They look like a reasonably well-balanced race, but ... eh.
(2) The new classes.
Now this is where I think the PHB2 shines. These classes seem
very well-balanced with the PHB1 classes, from my scan-through. They are also a lot tighter - that is, they are well-designed and very thematic. I didn't find any of them to be (as Plane Sailing said) fill-in-the-grid classes... All of them feel pretty unique.
Avengers are a very cool little class. I don't think they're Paladins+, since they have a very different shtick. Avengers fight and pursue their enemies and more or less ignore the rest of the party. Paladins work as a team, lock down foes, and enhance their party. I really like the flavor, and their balance seems right on - that is, they hit frequently with the right tactics, but do less damage than other strikers.
I have a Barbarian in my current game. Yes, they do frightening damage output, but I think it's fairly even with Rangers. They do a little more damage than archer rangers, but then again, archer rangers aren't in the thick of combat. They do more damage than two-weapon rangers when they hit, but have a lower chance of hitting. Also, countering the high damage are their low defenses. Raging barbarians will have a low-to-middling AC and a good Fortitude defense, but be weak on the others. Thaneborn Barbarians could actually do pretty well, but they also do less damage. The barbarian in my game drops almost every fight.
Bards look very cool. I can't give too much feedback as of yet, but I like how they worked in the skill mastery flavor, and the high versatility. I also like that they can easily rely mainly on their swords instead of blowing things up with sound.
Druids look solid. They also look pretty complex. Again, I want to see one of these guys in play before I give a final verdict, but I think their wild-shape ability was handled very, very well. Their powers are pretty convincing, and they look to be an excellent and versatile controller.
Invokers are probably my favorite of the new classes. I think of old-testament-style wrath-of-god type prophets and magicians, calling down the wrath of their god and summoning angels to their aid. They do seem to have some better control than Wizards, which is odd, but Wizards do significantly more damage over the course of their levels. I mean, even mid-level Invoker powers are only doing single dice of damage. I was worried they would overshadow Wizards, but from what I can tell, my worries were misplaced.
Shamans, I'm still waiting on. I like the idea of mainly operating through their spirit companion - it's like acting at a distance. I have never been very into the whole shamanic-type classes in the past, but this is the first I'd consider playing.
Sorcerors do, indeed, seem to be what Warlocks probably should have been. Their damage output is very impressive. Again, I would like to see one in play before I declare them basically Warlocks+ and relegate Warlocks to the dustbin of useless classes. In particular, I think many comparisons are ignoring how impressive the Warlock pact boons can get. Classes aren't just defined by their damage output.
Finally, I love Wardens from what I've seen of them so far. They are an unusual class, but I think they're a good role... I mean, "protector of nature" has been a fantasy trope for quite some time, and Wardens lock into it very well. I really like their Forms - they're like Barbarian Rages, but with some excellent flavor. They look to be tougher than fighters, but a little less sticky and dealing a little less damage. Again, I don't see them as a fill-in-the-grid class. I don't think it was a class anyone was really asking for, but now that we have it, I like it.
(3) Feats...
Well, I houseruled Expertise, but since that's about the only thing I have a major problem with, I consider the book a win.

As expected, the other feats are mainly for the new classes and races, but there are a few sweet ones that I think anyone could take and be happy with.
(4) Miscellany
I
love the Racial paragon paths. I particularly love the Human and Dragonborn paths, but the others are pretty good, too. About the only one I'm uncertain of is the poor Gnome... I don't know what class it would work for, to be honest. Anyway, I've been a fan of racial classes since Arcana Unearthed, so this short section is one of my favorites.
Equipment? Eh. It mostly fills in the blanks for the new classes, as expected. I'm glad Bards have songblades, but I hope AV2 or Dragon articles can give them some choice with them.
Rules? A couple of pretty big changes, including the Stealth errata and a little sentence stuck in the Saving Throws section that I think was badly needed. Still, not bad.
Overall, I'd give the book a solid A. It's one of my favorites so far. You could easily play many campaigns without it, but it's a good supplement and it does exactly what it is supposed to do.
-O