I've noticed a few cases lately where companies have released trailers for their games that have no gameplay, and even no connection to the gameplay. The earliest one that comes to mind is the Halo 3 trailers, like this TV trailer or this E3 trailer. However, that one at least has the defense of being (at least at that time) the third game in a trilogy, so you shouldn't really be buying it without having played the first two or you won't understand the plot.
The most famous example of a trailer not matching gameplay at all was the Dead Island trailer, which almost portrayed the game as being a lot more serious than it actually turned out to be. Most reviews after the release had the same conclusion - the game did not live up to its trailer.
Finally, the most recent example of this I've noticed is the Rome 2: Total War live action trailer.
(Description in spoiler)
The Rome 2 Total War trailer in particular, unless Creative Assembly plans a drastic change of direction, has absolutely nothing with how Total War games actually play out. The element they focused on is an extremely minor gameplay element - assassinations are basically a percentage chance event when you use an assassin on a character, with no prior planning required. Most of the game is spent looking at maps, or armies in battle.
Compare that trailer to the trailer for the original Rome. That trailer showed what was essentially a group of battles, rendered in game, that are totally plausible in game. Sure, it takes some liberties, such as using camera angles impossible when actually playing, and having unit compositions that no player would ever choose (like the all-cavalry julii army about halfway through), but there's nothing stopping you from having such battles yourself.
Sure, the Rome 2 trailer is more cinematic, but that's not why people watch game trailers. If they wanted that, they could watch movie trailers, or better yet, actual movies. People watch gameplay trailers to get an idea of what's in the game that they are considering buying. If you don't show any gameplay, or near-gameplay, the trailer has, IMO at least, failed at its purpose, no matter how good the CGI is, or how dramatic the events portrayed.
So what does everyone else think about cinematic game trailers vs. gameplay game trailers?