I am not a pessimist. The only thing negative from the trailer has to do with the graphics, and the graphics aren't completely bad as some people say...
Some graphical aspects are obviously improved: Many environment textures are crisp and detailed, the game seems to have actual dynamic lighting, and the old habit of applying a monochromatic tint (green on Fallout 3, gray/blue on Skyrim) is GONE, and thankfully the colors seem to be closer to reality, at least during the "now" parts of the video, because the "past" parts seem like a Pixar movie.
Now what is wrong with the graphics of Fallout 4, is the fact that some textures seem to not be detailed enough. Pay attention to what I say: I don't say that they are blurry, they are not, but they lack detail. And that makes some models to look cartoonish or plastic, something which is more obvious looking at the human characters.
Of course modders are going to make out 'realistic' texture packs immediately, so it doesn't matter that much if you are on the PC, but for console players, I guess the cartoonish feel is something you will have to cope with, if you don't like it.
What the trailer made me think of is this: Since the game doesn't seem to be needing too much of processing horsepower for its graphics, what will it be using it for ? Open cities ? Seamless transitions from exterior to inside buildings ? More NPCs on screen ? Larger draw distance ?