The screenplay focused on combining the integral plot moments in the story and weaving them together seamlessly, If i had not read the book, and was using pure movie information, i would've thought it was perfect due to the great fights, romance, and plot, but if you try to compare it to the book, you see that it misses a few important moments the book has, but as long as you treat it as a movie, Harry potter and the half blood prince, will not disappoint.