I think you're specifically talking about the cartoony look of that steroids guy we saw in that KS update and the negative reaction it got from many people.
Yeah, I must say was one of those people who didn't like the look AT ALL. Then again, you are right when you say that we should embrace change and not have a kind of negative knee-jerk reaction to it. However, I must admit I've always been an overall change-averse guy in my life, which I realize is not a good thing, but that's just the way I am.
Now, of course I expect changes in Shenmue 3. After all, the last game was released 16 years ago on the Dreamcast. And I do not want a Dreamcast game in 2017. I do want things to evolve, after all. Besides, that will be the positive side of us having to wait such a long time: Shenmue 3 will be much more advanced than it would have been, if it had been released for the Dreamcast back then.
Having said that, one of the reasons I really dislike that character's look is because Shenmue was very focused on realism. Real-world cities, with crazy attention to detail, real-world based weather (for Yokosuka, at least), realistic routines for NPCs (who felt just like regular, real-world people), true-to-life streets, shops, real-world product brands (well, in the Japanese version)... So, the whole thing always had a very "real" feel to it.
Not only that, but the previous two games already had a realistic aesthetic and, since this is just one continuous saga, I think aesthetic consistency should be important. It would look odd, if all of a sudden, when we dive back again into Shenmue's world, we find it to be all cartoony. It's not like, say, Final Fantasy, where each installment is a whole new thing, in a different world with new characters and new mechanics.
Not only that, but the screenshots we've seen of the game's setting (Bailu Village, that temple entrance etc.) actually look pretty damn realistic (though with stylized, exaggerated colours, which is fine and expected in a videogame), so I really don't see how a bunch of cartoony, manga-like characters will fit in those environments.
Again, of course characters will have to look different, this being PS4 and all, but they should be consistent with the previous' games realistic aesthetic (which I'm sure is easier said than done and that's probably why they're taking such a long time to show us the final version of Ryo and Shenhua's faces).
However, I realize that that steroids guy was still a work-in-progress model and that even the previous Shenmue games had some cartoony-looking, over-the-top NPCs and side characters, so it doesn't mean that everyone will look cartoony and I'll hold my judgement for now.
Having said that, maybe that will be the look they're going for and, if that's the case, I'll just have to come to grips with it. After all, Shenmue is Yu Suzuki's creation and if this is what he wants to do, then he has the right to do it and I'll just have to get used to it, because, obviously, I'm still going to play Shenmue 3 anyway (even if I hadn't already paid for it).
It is as you say, Spaghetti. If, even with a different approach to aesthetic, the game still keeps its core values and spirit, I'm sure I'll eventually get used to it, even if it takes me some time.
At this stage, it might just be better to accept that the models are not going to change drastically. There will inevitably be tweaks, as models in the originals were tweaked right up until near release, but the art style is basically set.
It all depends how you feel about those other NPCs revealed in the end of June update. They're a lot more restrained than muscle-guy, but there's still an obvious stylised aspect to their design. If you're okay with those, you'll probably be okay with 99% of the NPCs.
As for the environments, well, we haven't seen the full package yet. In fact we've seen more of the character models recently than the game world. After Gamescom's showing you'll probably know where you stand on the matter, but I don't really think we've got much to worry about.
Not long to go now.