Having read some of the more negative reviews on this site, all I can say is that they all seem to have the same complaint in common. Namely, non-acceptance of certain plot contrivances.
So let me say straight off: if you are the sort of person who didn't like Inception because it made no sense, or the sort of person who didn't like The Matrix Trilogy because it made no sense, or indeed the sort of person who didn't like any of David Lynch's films because (ahem) NONE OF THEM MAKE ANY SENSE...in short, if you are an incurable pedant, you will not enjoy this film and you might as well stop reading this review. Seriously, stop reading, don't watch the film and go calculate Pi or something.
If, however, you have an appreciation for tightly-edited, emotionally engaging, aesthetically pleasing cinema with a brilliant soundtrack and at times breathless pacing, please allow me to take a few minutes of your time.
Hanna is the story of a teenage girl who lives in total isolation with her father. She has vague memories of her mother, and these memories, combined with her (literally) encyclopedic knowledge fuel her desire to leave the relative safety of her father's protection in the frozen hinterland of northern Finland.
In a way, I don't want to say any more than that. If you've read the other reviews on this site that give away more, then I'm very sorry for you, but if not then suffice it to say that her father's motivation for keeping her in this state of isolation appears to be protection, combined with a desire to train her in survival/assassination skills, in preparation for...well that would be telling.
Of course, you don't need me to tell you that she leaves her father's protection and the story proper begins. As Chekov said "One must not put a loaded rifle on the stage if no-one is thinking of using it" and boy, does that rifle get used.
Saoirse Ronan is brilliant as Hanna. At times seemingly invincible, at others pathetically vulnerable, owing to her complete inexperience of the world. We see the world from her unique perspective as she struggles to understand non-familiar interaction, the natural ease of recreation and even the basic electrical appliances that we all take for granted.
The story moves us from one location to the next, painting a rich tapestry of colour and culture, whilst simultaneously (and somewhat comically) contrasting Hanna's desperate need to traverse these territories with the bourgeoisie's seeming obsession with "experiencing" as many of them as possible.
The acting is solid throughout. The only truly great performance comes from Ronan, but Tom Hollander, Cate Blanchett and Eric Bana all turn out good performances that serve the picture well.
However the true credit for this film has to be laid at the feet of Joe Wright. None of his previous films could possibly prepare you for Hanna. Wright's mastery of both a tight, intricate plot such as in Atonement, combined with his incredible skill in making this beautiful, thoughtful, action-packed coming of age story mark him out as a director of real class.
It is true that Hanna suffers from a few plot holes, but that plot is delivered in such an appealing, exciting and above-all entertaining film that anyone who isn't compiling continuity errors for some god-awful TV programme that relishes in the fact that THIS ISN'T REAL LIFE, IT'S ACTUALLY ONLY A FILM!! should have a blast letting this film take them along for the ride.
If you want reality, watch a documentary. If you want a very good fiction, watch Hanna.