I think it's too early to be disappointed by a 3 minute trailer, but I understand if it's not your cup of tea. But if this is really Kanto, they have to put some effort into what started it all. I doubt they would waste this opportunity to make Kanto look good since we haven't seen it in years. (minus some cameos).
As for the style, the game would not have looked nearly as good if it was on the 3ds and there are features that obviously wouldn't work as well such as the hop-in co-op. And while it isn't super pushing the limit of the graphics, it doesn't mean it's lazy.
The game looks nice. It's not groundbreaking, but it doesn't need to be. It still looks like Pokemon and that's fine with me. Say what you think about the chibi style, but it allowed for a lot more detail to be put into the environments in X and Y and ORAS. (Content is a different argument). I honestly prefer the Go models to the 3ds ones because the ones in the 3ds look so much more desaturated. Here it looks way more colorful.
Once again, this is game to appeal to people who want a more casual experience. It makes more sense that the art style would look cuter. The chibi style makes sense to me because that's what tends to get younger people's attention, cute things.
I'll hold off on my graphical complaints when gen 8 comes. If gen 8 doesn't look like SuMo, then I'd be inclined to agree with you, but I'm not at the moment.