I think DICE showed a lot of people how you do a demo that both does not waste a lot of development time to make and gets people pumped up for the game while not spoiling too much of the game (many games either offer too much of the full game's gameplay or they do and end up spoiling the full game which awaits for purchasers in the bargains' bin).
It is not an easy thing to do, using the same level showed since the first E3 appearance could have been dangerous (people not interested in even booting it up), but it does provide you some great benefits:
1.) creating a demo is usually a lot of extra work for developers which takes away time from the game's development time and usually comes out much closer to the game release, sometime after, or it comes using a quite old build of the game which IMHO is bad... when you have to tell people "hey this is an old build the graphics/gameplay gets much better in the final release" you are doing damage control and you should not have to do that. This demo is based on a well tested, polished, and tight level with which they have been demoing the game since its first unveiling.
2.) this game looks very good, it is a beautiful to watch, but for how awesome it might look it is actually even better to play it and thankfully for DICE the videos of the game have given us thus far a kind of curiosity for this unique first person "parkour/adventure" game so people did want to at least try the demo. Even if you played the demo just to "try it out" and maybe you started it feeling a bit disappointed in getting the "same ol' level" you have seen someone else playing a thousand times already (not my case btw), by the time you have finished the tutorial and started playing the actual level you do not care anymore about what level you are playing in... you are IN the game so to speak
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No game video can do this game justice... only a demo can and IMHO DID. This game is a must buy IMHO (if you can afford to purchase it during this packed season) and should be offered on PSN too as a full download (like they did with Burnout Paradise) for a somewhat discounted price (the advantage of digital delivery for EA would be that the game cannot be resold for Gamestop feeding the used sales market thus they could choose to price the PSN release at a lower price than the Blu-Ray version).