The demo started up at the same point in the game where you first start being able to start battles in the game. The demo first forced you to go through the menu and look at the "help" topics before it would let you progress - something that at least Pro didn't require. You then get to have your first monster battle, which is against a slime. If you don't scout it and defeat it again you are forced to fight more slimes until you scout one before the game will let you progress any further-which WAS in the main game. My sister, whose never played a Monsters game before, got frustrated and annoyed at the game at this point due to the high level of forced hand-holding. But once you get past that point the game continues on exactly like it would in the non-demo version.
Other than the normal changed pun names and accents inserted in the game, the small amount of text that the demo showed seemed to be a decent translation. This game also has the benefit that monster names at least can be entered in Japanese as well as English, which helps make the names stand out from the normal text. Suggested monster names weren't all that clever, but since they aren't forced it doesn't really matter. The game was obviously not pro due to what monsters were present and where along with the colorization differences that pro brings to the main character and the giant worm.
The great thing about Joker 2 is it really gives you the sense that the monsters that you see on the island are going about their normal lives in the wild. The way they move, or interact amongst themselves helps to bring the game to life and helps to characterize the monsters that you will be befriending. The maps are fairly inventive as well, and create a good atmosphere. At the same time though, they aren't particularly challenging, and were obviously created so that a child could still navigate through them successfully.
The demo ended either when you run out of time (the time limit isn't shown) or you reach the next story point. The demo was never full of people (unlike the Wii Zelda game) but a number of people came and tried the game for a bit while I was playing. I don't know how well you could hear the music and sounds from the game either because the dance game next to it kept on blaring on about Barbra Streisand.
As a more general review of the game, if you like the previous Joker you will like this one as well. If you didn't like the last one though you might want to give this one a try at least, because the immersive environments and monsters add a lot to the Joker world. If you love the monsters in Dragon Quest you'll find them characterized more fully than any DQ game before.