Sure, they look really cool, and can thrill the imagination. But they have ZERO bearing on the actual game, and they show nothing of significance about the gameplay (you know, the bit that actually matters?). The more slick and impressive one is the more I think "How much money was wasted on making this rather than being invested in something useful for the game?" Rather than getting me interested, these things are starting to actually turn me off. They seem to be more of an advertisement of how much a game studio's priorities are in the wrong place; how they want flashy imagery to excite people's interest rather than the merits of the game speaking for itself.
And in the case of TESO, especially, when so little of what we've heard about it is anything significantly concrete about the actual game. When your potential playerbase is already skeptical and more interested in finding out whether or not your game is yet another amalgam of tired MMO cliches in a new skin, showing off a fancy 6 minute cutscene trailer illustrating cool stuff that nobody ingame can actually do, most likely, is not a good idea in my opinion. What does this stuff have to do with what people will actually be able to experience? This looks like it'd be a cool movie but tells me jack about whether its an interesting game.
Overall, though, MMO studios need to stop with the gimmicky PR garbage and focus on the quality of their product, not the volume of their hype. Because as excitable as many MMO players can be, I think we've reached a critical level of jaded low tolerance for the same old crap in a different box. No amount of fanciful CGI shenanigans is going to save your game if it can't actually deliver. I swear the priorities of AAA MMO studios nowadays are really backwards.