Deathly Hallows I is more dramatic than the section of the book it presents. If you haven't read the book, you will miss out on why the story goes this way. What a shame that would be.
The "Half-Blood Prince" installment of the Harry Potter movie serial is an intermezzo, a slower-paced bit of story tellling that may not hold the interest of the casual viewer. It lacks the compelling plot of the previous installments. Those who know the books will be disapponted at the amount of material left out by the movie makers, and some will wonder how they will tie up the ends in the succeeding movies. But it was an enjoyable night at the movies, and I think you will find it worth your viewing.