Well, I liked the fifth film. But I got to this conclution after much consideration. At first, I didnt like it, at all. But then I watch it in Imax 3D, and I like it a lot better! David Yates, in my opinion, did a good job, he was at least bettter than Mike Newell and Chris Colombus, in my opinion what Yates is lacking of is experince, thats why, after seeing what worked and what didnt in Order of the Phoenix, I am quite sure he will do a good job in Half Blood Prince. As for the visual effects.... the effects were considerably better than the first four films. They were quite decent.
You are right, Chris Colombus did an amazing job for the first one, he introduced the world in an incredible way, but I dont think he should have stayed for more than the first two. His work became repetitive. My favourite director of the series is Alfonso Cuarón, that man really did an incredible job for Prisoner of Azkaban. I wished he was the one directing Half Blood Prince.