I'm not really sure what I think about it yet. I thought the last book was sucktastic and I've already had most of this book "ruined" for me by spoilers online. I already know who croaks for instance and which dastardly guy did the deed. I know about the debate over whether snape is evil or good and a lot of the other minutiae. The fact that the basic consenses seems to be that this book is a giant prequel for the last book dosen't actually fill be with a lot of hope that i'm not going to loathe it.
Overall, it seems that the tone of the books is certainly getting more serious. I wasn't expecting the whole draco breaking potter's nose thing, and the confrontations are growing more serious. The odd thing is...on one level, rowling clearly wants us to feel this rising and immininent threat due to voldemort's return. She goes out of her way to repeatedly stress the danger through devices like the weasely's family clock and the repeated news reports of deaths and attacks. We're supposed to believe this, and yet we don't see the characters taking things seriously at times. Harry more or less deduced right off the bat that malfoy is a death eater. It would be their duty quite frankly to catch him unawares, rip up his sleeve and if necessary once the mark is revealed, to off him. You don't simply go on and let him prance around as he wills. What's the worst that could happen if potter is wrong and he jumps malfoy, pulls up his sleeve, and reveals nothing? 50 points from griffindor? Detention? Who the fuck cares? The entire world is falling apart. That would be a small price to pay for possibily unmasking a death eater.
If all death eaters are thus marked, I'm surprised the ministry hasn't just called for mandatory strip searches already.