The FILM Hannibal is actually pretty decent. I have not read the book, but the friend I saw it with explained that there are many differences between the two. One MAJOR difference is the ending, which I won't give away, but - IMHO - is much better than the one in the book.
The key to enjoying this movie is NOT expecting to see Silence of the Lambs again. Essentially, they have taken the characters and history of the original, and made an entertaining movie that plays out more like a comic book than anything else. It is not mind blowing, there is no major suspense, but it is generally a fun watch.
Julianne Moore is excellent in the role as Special Agent Starling (rrowr), and the fact that she replaced Jodie Foster (who supposedly turned down the role because she didn't like what happened to her character) actually helps to create a mental separation from the original. This enabled me as a viewer to treat it as a separate work. Comparing the two now becomes more like comparing Bond Films that starred different leading men.
Anthony Hopkins was excellent, as is to be expected. Not much to say there, except he plays the same character, but he is slightly more fallable due to age. Ray Liotta does a great job of playing a jerk FBI agent who gives Starling real trouble. And Gary Oldman even has an uncredited, but major, role (see if you can find him).
All in all, worth seeing in a theater, but like I said before, don't expect great art. Just expect a fun watch. One warning though, the gore level is kinda high. At times it is on par with Texas Chainsaw Massacre in that department.
Cast and crew (Thanks IMDB):