Less seems to happen in this book, although there is a whiz-bang ending. The 'theme' or 'threat' Rowling uses to tie together the events of the school year is weaker than previous, but still has interesting consequences. Too many flashbacks. Too much snogging. My main complaint is that the bok has a half-finished feel - the story arcs aren't quite there. Rowling is usually an expert at pacing, but it seemed like fewer neat things happened and the energy was just not there.
Plus there was a typo on page ten.
I thought Harry's romance with Ginny was handled significantly worse than his romance with Cho, which, although excruciatingly painful, was at least realistic. The way H and G finally got together was, frankly, a complete cop-out, and the break-up at the end did not ring true.
I'm trying to find more to say about the book, and I'm having a hard time. The dealie with the Horcruxes was intriguing but not really a complete arc. The whole Snape thing seemed contrived. And once again, why not kill Harry? Because Lord Voldemort wants to lock him up in a cell with a single guard? The only theory I've heard that's interesting is that Harry somehow is one of the Horcruxes. It'd better be that or it better be a super-secret-special-triple cross because, well, otherwise it's just a bit lame.