This movie is quite surprising, considering the time period it got made in. You have to realize that there wasn't really such a thing as the action genre yet at the time, at least not in the way we now know it.
In that regard this movie really feels ahead of its time and perhaps can even be seen as a trend-setter. It's a Kung Fu flick, featuring lots of sword fights and all kinds of adventurous aspects. This is a genre that truly became popular much later, in the '70's.
It's also a movie that goes very over-the-top with all of its action. It's almost done in a cartoon-like kind of way. Quite ridicules to see at times but also at the same time it's what giving the movie its style and helps to make it the entertaining movie that it is.
It's truly a movie that thrives on its action moments. You obviously shouldn't watch this for its story, that is kind of simplistic and formulaic in the first place. It's the action that makes the movie entertaining and luckily the action never disappoints neither. All of the sword fights are quite spectacularly done, though you should all take it with a big grain of salt really, since it's all obviously something that could never happen in real life.
But it's not just the way things got choreographed but also really the way it got shot. That to me was the biggest surprise; how dynamically the movie got shot. It features some great camera-work, as well as some nimble editing that make the movie fast paced and often spectacular to look at. It feels and looks like a true action movie, even still now days.
It's also quite surprising to see a female playing the main lead and hero of the movie. She's the one who does the most fighting and has some of the most impressive skills. She puts a lot of the male characters to shame in this one and also apparently became popular enough to spawn a sequel after.
Simply good entertainment and a great accomplishment of a movie, especially considering that this movie is from the earliest days of the Hong Kong martial arts genre.