[quote name='Cantaloup']Same here. From the demo I don't really get the appeal. What am I missing?

?[/quote]
The Demo really isn't as exciting as the full game (duh), but you get the gist of it. Rez, gameplay wise, is strongly about trying to perfect your run through the stages, getting all the items, killing every enemy, and doing everything the stage offers you.
Beyond Gameplay, it's about a combination of the pace and flow of the images and music. The game attempts to bring all methods of interation with it (through sound, visuals, rythm, etc) into one coherent experience, and general concensus is that it accomplishes this better than just about anything out there.
For me, Stage 5 and the bonus features are just as great as, say, Portal. Rez is one of the rare Xbox Live games that was made as a full console release that's now being offered for an exceedingly low price. It encourages and rewards multiple play throughs, too. (More Xbox Live Arcade games need to reward you like this.)
If you open your mind to it, you should be able to appreciate it.