It's not gravity Blackbeard said that his darkness is gravity or that is how darkness is shown as being able to pull things in and release them. Apart from him being the real captain of the Roger pirates and the actual first Pirate King, I do hope Doflamingo shows up in the next 2 or 3 arcs, I really want to see him fight Luffy. This arc isn't going to be over anytime soon unless it's like Water 7 and ends up starting a new arc on another island but it seems like we are at the point comparatively where CP9 just beat up the SH's at Water 7. I think the turnaround will happen soon and if not it will happen after Virgo does some more damage.
Also I'm 99.99% sure Virgo's attack was haki, it wouldn't make sense for it to be something else. However why his haki shows the blackening like Luffy's while Shank's or others didn't doesn't make sense. Unless blackening = denser haki power, like it can be used to the level of Luffy vs Pacifista or Luffy grabbing Smokershigi's arm or to the power of breaking iron shields and destroying island sized boats.
Lastly opinions on the arc so far? Compared to the mini-Reunion arc and FI arc? Overall? When Law appeared I was like nice, the YCB annoyed me, CC's gassing people and not fighting is annoying, but now that I know Virgo and Joker are the stronger of this arc's villains and CC himself wasn't thrashed by the haki hits like Hordy I'm saying it's about like Alabasta arc where it has annoying parts but you know it's going to end with epic battles and the plotline is pretty good.