I just played the demo about an hour ago and it was really good fun. The world from the beginning just draws you in. The dialogue and cut-scenes are made interesting with humour and the fact that Jack Black just adds that extra touch to the game. Never once did I think "Man, this cut-scenes going on a bit too long, I wish I could get back to the game." Even the cheesy lines 'Eddie' comes out with every few seconds aren't in the least bit annoying, but I might change my tone by the end of the game.
Either way, I'm really excited for this game. Seems like videogames haven't been fun recently.