Yes the drawing has changed since the beginning of OP, but after all these years, don't you think Oda knows perfectly what he is doing when drawing the two last pictures of Ace with such a ressemblance with Shanks face ?
What does this latest chapter bring to the story ? We already knew, since several chapters, that Ace would be defeated (except for some blindfolded Ace's fans). We already knew that this would be the beginning of the raise of BB. So what does this chapter carry ? Yeah, some info about BB powers (some hope because he seems to be vulnerable to direct hits, and lot of fear because we can't see how he can really be defeated).
But above all I think Oda used it to bring a new important information, which is that Ace is Shanks son: all these years, we have been asking ourselves who Luffy and Ace's parents could be, recently Oda revealed a lot of things about Luffy. But nothing about Ace. No mention anywhere. Garp comes, talks about his son Dragon - Luffy's father - talks about the four emperors, the government, and Shanks. And not a single word about Ace ?
The only "problem" I see is that Ace is subject to narcolepsy like Garp which most probably makes him one of his grandsons… If Shanks is is father, then there are 2 possibilities:
1- Shanks is also Garp son ? That would make Shanks and Dragon brothers, which I don't believe. Mostly because Ace and Luffy have different family names.
2- Garps also had one daugther, who had Ace with Shanks. It looks way possible to me, because we know that Garp doesn't really like Shanks... Could be because of his bad influence over Luffy, but also because of his relation with his daugther...
PS: come on, we're all expecting to know of a female in Luffy's family !
PS2: or even a female "D" !