Summary: House of Flying Daggers is eye candy best viewed with one's brain turned off. It had potential--some interesting plot twists, entertaining martial arts action, and rich, beautiful colors throughout--but was ultimately too completely divorced from reality to even approach the level of a movie like Crouching Tiger Hidden Dragon.
WARNING: Some spoilers follow
A quick comparison to Crouching Tiger will illustrate some of the problems:
CTHD: Four extraordinary individuals with incredible fighting skills and limited supernatural abilities (primarily the ability to become weightless).
HoFD: A horde of extraordinary people with incredible fighting skills and many supernatural abilities (including a small army of people who could run full speed through the tops of a bamboo forest; a guy who could shoot four arrows and have them all arrive at their targets simultaneously, each embedding itself in a person's clothes without hitting the person, in spite of the fact that the people moved around quite a bit after the arrows were shot; a whole group of people with magical dagger throwing ability; etc.)
CTHD: One extraordinary weapon (The Green Destiny) with no supernatural abilities--just incredible craftsmanship.
HoFD: Tons of daggers that can change direction in the air, and that start of rotating, but stop the rotation and point toward their target in the air.
The biggest problem I saw in HoFD was the overdoing of the supernatural maritial arts. The early scene where Mei pulls the captain's sword out of it's scabbard with her long sleeves is a perfect example. Had she done that, and then met the sword half way, and proceeded to fight with less supernatural abilities, it would have been a fantastic scene. Instead, she pulls the sword from it's scabbard and proceeds to take numerous swings at him with it while it is held perhaps fifteen feet from her by only a silk sleeve. It was just too far from reality. A hero with unlimited powers is less interesting than one who is either vulnerable, or who has some special powers, but mostly depends on superbly developed natural skills.
I was able to enjoy the movie because I recognized early that realism was not a major concern to the filmmakers, and with effort, was able to largely close my eyes to these flaws. Had the movie makers either asked themselves what they should do after discovering what they could do, or made greater effort to make what they could do more believable (making the daggers fly straight and not change rotation in the air would have been one big improvement), comparisons to Crouching Tiger may have been more apt. House of Flying Daggars in eye candy. Go into it expecting eye candy and little else, and you may not be disappointed. Just don't watch it expecting a classic.