I know you worked hard on it, and the ideas and design were all good, but the animation and the music didn't quite cut it.
The music suddenly cut in and it was suddenly a battle- no buildup at all besides "Except one survived", not even a "whenever years later", and the sudden music didn't really help, or match all that well. I know this bit might just be my opinion, but it just seems off-key to me.
Along with that, the animation looped quite a number of times and repeatedly used the same view techniques. Instead of following the person you're focusing on with the viewpoint shaking violently, why not zoom the camera out and watch him run across or fall off the cliff instead, to give it a cinematic feel? It's not terrible, and as was stated by another before me, a lot of animators do it, but it just felt like it was one big repeat with different images.
On the positive side, I personally liked the drawn element- each pose is done with detail, and the overall design is excellent. The ending cutscene was quite well done, as well as the Neptune- or Poseidon-like status of the 'big bad' (the sea gods of old times were always high ranks, right?).
Overall, it was quite good with the artistic ('still frame') aspects, but it desperately needs work on aspects more unique to animated pieces.
Are you sure flash is what you want to do? You seem like you would make excellent comics or comic books.