It's probably not worth $10, but, then, what dlc is? As far as gameplay goes, the dlc is harder (a relative term when talking about such an easy game) and even more linear than anything on the disc. The story, however, is a weird thing...it actually made me angry at first because it seemed to really scuttle the ending of the game which is actually quite beautiful: Elika's justified rage at the prince making her sacrifice a meaningless act, the prince 'maturing' by going from pure narcissist to just plain selfish (in the name of love, of course) - something very lovely and heartbreaking about it. The dlc kind of undoes how satisfying the game's ending was (like i said, to the point of anger for me), but the ending of the dlc wound up being very satisfying as well - an unexpected resolution that (somewhat) restored the tragic satisfaction (a weird thing to say, i know) of the game.
Wow, i wrote way too much about this. Anyways, the dlc isn't worth it gameplay-wise, i would say, but if you're hooked on the story THAT MUCH (i was hooked on Elika, so the dlc was a no-brainer for me) you might find it very much worth the price.
Message me here or via PSN if you want to work on the trophies for Clan of Champions