A teenage girl on steroids trained, as a ninja, with a bad attitude and a desire to humble testosterone hyped men with her feminine prowess, quick wit and no nonsense method... this is pretty much what you have here.
It's not terrible but you only need to watch the first five minutes to realise this is pretty much the sequence of events throughout the whole film. It would be a pretty good film for kids but for some of the scenes which are not so much excessively graphic, but too violently depicted for the younger viewers.
It was entertaining in parts and obviously isn't a film to be taken too seriously, so I don't really understand some of the exaggerated negative reviews. These seem to come primarily from people with an axe to grind on the female lead having pseudo super powers. Well these people need to get over themselves and not transpose their feelings of patriarchy on everything that has a dominant female lead. Its a fun film for the most part and for what it offers, it's been fairly well done.
Don't expect any highly choregraphed fight exchanges, this isn't a Jet Li movie. It's a lot of clever camera work, strategic positioning, and bad guys dancing around menacingly as they wait to be disposed of in an orderly fashion, so if your sceptical about some of the battle scenes, don't make a fuss, just try not to grimace too much as the ladies around you whoop and cheer as the fight scenes unfold.
Though It is generally watchable, the reviews giving it top marks are as equally ridiculous as those giving it the lowest scores possible. Its an entertaining movie if your looking for a heroin feminine enough to pull of the Cinderella look whilst capable enough in her battle skills to warrant a place on the 'Mortal Kombat' line up. The acting is reasonable, the script a fairly hackneyed, and the paper thin plot does little to disguise where it's going from the onset, but at least it never attempts to hoodwink you into something your not prepared for, or sell you on a screenplay you didn't know was coming five miles out from the title.
I'm only surprised the film set is so elaborate, and some good work has been done with this aspect of the movie which lends some considerable credence to the screenplay. Ultimately it's a shallow well worn tale without a lot of new substance to flesh it out save the 'Nikata' princess angle which wears a little thin after the first ten minutes. Suspend your disbelief well before seating yourself comfortably to watch this one and I'm sure you'll be fine. It's good for entertainment value if you like this sort of thing, if not you'll probably hate it.
I think 4/10 is a fair score from my perspective, but I think I'd go to a 6 maybe even a7/10 at a push if its your kinda thing.
That said, lets be clear, this film is no masterpiece and anyone trying to convince you it is is trying to sell you magic beans.
Hope this helps.
Tingnan pa 
