I thought it was awesome. They had to show how badass Dayne was, since he was arguably the greatest swordsman of all time according to GRRM, so I loved it. They actually did show his sword Dawn too :
In the books it's a great sword made of a meteorite (falling star) that is supposedly very light in contrast to regular steel, and that it has a pale white glow, so perhaps that would look weird on film. In any event, they certainly got the point across that he was a pure badass and that Ned would have been a goner if not for Howland Reed. Sean Bean is kinda weird looking maybe they couldn't find a young actor that resembled him, which is often the case on TV/movies when they do flashbacks with younger different actors. At least they had the same hair style lol