Many may not consider themselves too interested in video game marketing, it's best not to downplay its importance within the industry.
After all, events like E3 and Gamescom have only shot up in importance, because they are often the defining moments that convince players to pick up a specific title. Although the quality of the game decides its final judgment, great marketing may very well be all it takes to get your preorder.
This is where marketers earn their paycheck and more often than not, they are masters of influence. That influence comes in the form of developers/publishers who are working to ensure you forget major disappointments in their past or someone completely unknown selling you concepts rather than something actually plausible (i.e. most cinematic trailers).
Even if your inner skeptic kicks in, that optimistic, more excitable part of your brain may end up being too powerful.
Many publishers are aware of this and use it to their advantage. It's sadly what leads many titles to great financial success, even though their quality does not warrant it. Whether they're rushed to release or marketed as much more than they really are, it's gamers that end up getting burned. These titles are ones that mis-marketed themselves, one way or another, to get players' money.
Malicious or not, they were all experiences that didn't live up to what was shown.