I feel mixed.
I'm not the biggest fan of the "evil twin" thing. I think it would have been more interesting to just have Shanks be working with the World Government for his own reasons. And maybe he still could be. But, why bother giving us a "evil twin" in the first place if he's not going to confuse the audience?
But, I am curious where Oda is going with this. There's probably some reason Oda's doing this, and I'm willing to see how it plays out. Given all the stuff with the clones and Seraphim and now the identical twins, Oda does seem to be setting something up.
Personally, I'm wondering if this is all set up to reveal that Nika had a twin, who's partially the reason for some of the stories about being a God of Destruction. Maybe Nika had a twin brother...let's call him "Zika". Maybe "Zika" is the source for Blackbeard's Darkness Fruit. So maybe, all the conflicting stories we've heard about Nika are the result of there actually being TWO of them this entire time. I doubt it, though. As sinister as that smile on our new look at Nika felt last chapter, he was still carrying a "sun shield", so it's probably still depicting a "good guy". But, still, keep an eye on Nika. I do feel like "Zika" could potentially be a thing.