Yes it is worth the price, the amount of content packed into the game is more than some console games. There are tons of items and the character diversity is really good. Despite what some have said, the gameplay is far from shallow, it requires a lot more thought when fighting and button mashing gets you nowhere as you are severely punished for doing so.
It's quite a refreshing departure from traditional fighting games and it's melding of fighting game and RPG mechanics are pulled off excellently. The beginning of the game is admittedly a little slow, but as you level up your characters and progress through the story, you gain more skills as you level up and the story gets rather interesting. The story mode alone will burn away 20 hours of your life, and leveling/mastering characters and their abilities makes fighting worth something.
If you've already tried the demo, then go pick up the game. The demo itself is nothing bore than a bare bones look at the game and the arcade mode. The actual game can get a lot harder and there is more to it. It's worth the price, with the amount of content in it and hell, simply because it tries to bring something new to the fighting genre...a genre that feels like little has changed since it's advent.