Expectations seemed very high for many but you have to understand that this film was never going to be produced the same way the series was.
Also, you need to be a fan of the whole series to understand who all of the characters in this film are. As a stand alone most won't get it and didn't get it by the low rating.
As for the film it self, It was a great way to demonstrate how Tony saw the world in his upbringing and makes you appreciate more the elder Tony and why he was the way he was for 6 seasons. Vera Farmiga played her role perfectly and so did Micheal Gandolfini. His mannerism and facial expressions are a mirror image of his father James. Outside of the fact this was a movie, the ending leaves you wanting more and it's as if young Tony now sees what world lies before him and what his destiny will be. A sequel to the prequel would make sense, if not even a short series on the growing pains of young Tony as he grows to become the leader he became.
As far as Ray Liotta goes, that is where one star is taken off, he added zero value to the production and storyline and to be honest they could have given Micheal Gandolfini more time on screen instead of wasting it on Liotta.