Particularly, it's the magic items that got my attention. They're much, much lower power than in previous editions (besides being occasionally nonsensical, like a literal halo you can apparently get from piles of treasure). Some are so low, in fact, that I strongly suspect power creep is going to overtake them within a year, and we're going to be seeing traditional D&D items sneak back into the game and completely screw with existing balance. I mean, there's a 3-million gold item that grants invulnerability for one round a day... potentially a lifesaver, sure, but no more so than class powers that come at a third of its level.
Ritual Casting also got a raised eyebrow. It's not that I don't like it -- as far as mistakes go, it's my favorite in the new edition. I love the idea of any class being able to cast spells, and it never made any sense to me to make it as impossible as it was in earlier editions. This is the logical extension of allowing wizards to wield longswords, which took damn long enough on its own.
The problem is that it's easy. Really easy. I foresee no real difficulties for any character acquiring a pretty respectable library of rituals... and as they stand right now, that's not that bad. But as with magic items, feats, and so on, power creep is inevitable, even if only by providing more and more options. And since it only takes any character one feat at most to be able to cast any ritual they want within their level range, there's no control in place -- other, of course, than the laughably irrelevant economic costs. In the Monty Haul genre, cost inflation is almost invariably met with reward inflation. They would have done better to take WoW's advice and simply make one gold actually worth something.
And if the MMOs this game clings so dearly to have taught me anything, it's that their problems are resolved by over-correction. I don't know what's more potentially disappointing to me... the idea of 'cash sink' rituals, or the thought of class-specific rituals, which would diminish what makes the idea so good in the first place. Ah well.
My final thought: The hatred 4e's picked up from some corners is entirely undeserved, but I think the similarly-scaled enthusiasm is premature. The game plays a bit better than 3.5, but it's lost a lot of the richness of that game; doubtless things will improve as supplements are released through the new pay-to-play network, but it's too easy to see the game crashing itself as well.
And I really have no idea how they're going to bring Forgotten Realms into this.