Trailer?
To begin with, well done for making a fluid flash. Although this is going to be a "tale of love, bravery and rivalry" (is that right) I still have no idea of what is going on, other than people running and fighting with glowing swords. In a trailer, unless the title is obvious (example being that AvP trailer where all we saw was predator's armour), the viewers won't really know what the subject matter is. This may affect how they view the trailer as well as their interest in the actualy full version.
As to the technical bits, the animation was alright, it was fluid with an interesting drawing style...apart from the fact that it was drawn like one of those shitty japanese cartoons where everyone has stupid long hair and massive eyes. I think that is the worst thing to happen. War seems a better development than this style of animation - although this inclusion of subjectivity negates everything I have said and will now say. It is up to you to acknowledge or ignore what I write. You have probably drawn most of the full version now in that style, but if it is not too late could you please change it? You may disagree (mind you, taking this flash into account, you most certainly do), but this style is for me a travesty, an overused hideous abomination. Not your flash, just the notion of such animative techniques.
On a lighter note, there were some instances where someone's eye was over their hair, which looked odd. The music was rather dire, reminded me of Pokemon (sorry :( ) or something similar. In such fast paced scenes it is best to use music with no vocals, to place emphasis on what is happening, while the music can obviously increase its effects or highlight the speed or chaos etc.
A good use of colour too, a vivid display which probably hints at the action and many characters, which, sadly seemed to look very similar. It was good in the ways that are not included in the points above, so well done, you'll get a protect point from me, please reply telling me what you think of the animation technique please. Thanks and I hope this has helped, it is meant as constructive and not personal,