I think that RPG demos are usually bad. They're never enough. The only one I liked recently was the Etrian Odyssey IV demo because it was just the first section of the game, and let you carry over your save file to the full game.
But RPG demos are usually just a quick taste, and the way I see it, the people that already decided to buy the game are just excited, so the demo calms them down a bit. Like an appetizer.
That's the case with me and Bravely Default. Its demo is up on the 3DS eShop today. Like you, I'm super excited for the release of this RPG, coming this February. My day has been cleared for this demo.
What's neat is that this demo features a side quest that is not available in the full game.
Enjoy, fellow RPG fans.