With the arc slowly getting to the fights, I feel it's a good time to do an overview of the arc so far.
First big thing to talk about is how the arc has been done on a chapter basis. It's been a lot of switching around with no character usually getting focus for a single chapter for the most part. Even in chapters like Law v Doflamingo V Fujitora, or Luffy's fight in Coliseum had 100% focus. While it has resulted in a number of stuff having less screen time, it has allowed for more stuff to happen in a chapter. This arc would be longer if it tried to focus on each group per chapter, or it would be the same length but the locations characters would be at would jump around a lot each chapter. By doing chapters by showing each group, the location jump is less jarring for each character, as we can assume during the time frame since we last saw the character, they got to their location. Some things could be done better, and it's safe to assume that if Oda will use this style again, he will have learned how to better utilize it.
A number of the Straw Hats have contributed in some way this arc, whether big or small. Sanji was the one to find out about Doflamingo's intentions, and got the others to know about it before allowing the deal to happen. He also saved Nami, Chopper, and Brook from Doflamingo. While not part of the arc anymore, we know he was fighting off Big Mom's crew before heading to meet Laws crew. Ussop played a big role by reversing the effects of Sugar, which allowed a number of Gladiators to team up with Luffy. Franky has helped with letting the others sneak in, and is playing a role to destroy the SMILE factory. Robin has been playing her usual role of relaying information, and it looks like she will be participating in the fighting. Brook beat Jura by using his wits, saving the others. The main ones that haven't really contributed, and won't, is Nami and Chopper. The rest of the Straw Hats on Dressrosa still have a chance to do more.
We have been introduced to a number of characters this arc, ranging from some named fighters from various countries, to one of the new admirals and the second hand of the Revolutionary Army. While a number of the Gladiators have had time to shine, a bunch of other characters haven't has their chance. Some will probably not get time shown, mostly a lot of the Gladiators, since there are to many to give screen time to if this arc isn't to keep going longer. The main three that haven't been shown are Burgess, Fujitora, and Sabo. While they might get a little more time, these characters are around more to get readers looking forward to future events. We want to know what BB's crew is up to, especially since they were talking about Kuzan. Fujitora is there to get people wondering more about what will happen with the Marines and WG, especially with the Reverie. Sabo is there to show a bit of what the Revolutionaries do, and to give Luffy more connection to the group.
Last, but also very important, are the plot points that have been brought up. We've seen a lot of what Doflamingo does, and at this point how much people suffer. Doflamingo runs a number of businesses, which cause lots of suffering. He does all this to obtain power so he can get to the top. This makes readers want him to lose for two major reasons, the fact that he's a terrible person, but even bigger is that when he falls, it's going to cause a much bigger ruckus than almost any other event in this manga. Some readers feel there is a lack of tension in what's going on, and that's going to be quite subjective. However, between seeing the suffering of the royal family, the civilians with Bird Cage up, as well as the suffering of the Tonattas, the readers have a number of ways to sympathize with a group to want to see Doflamingo fall. All this allows us to look forward to the fights as Doflamingo's empire is slowly crumbling.
After typing this up, I have to say this is a pretty great arc. It's not the best, but depending on how the rest of it goes, it could go up there as some peoples top arcs. Like any arc, it does have it's faults, and how big they are is determined by the reader, but until the arc ends, there is a chance it can be rectified. The above information in no way is saying that all that stuff is good, since readers are split on a lot of it. It's there to give an overview of what we have seen in this arc. There are details that I may have missed, but I feel this gives a good overview of the stuff we know.
It will be interesting to see how this arc goes from here on out. There are many expectations people have, which many will most likely not be filled. I personally look forward to the final confrontation, and wait to see what the effects of this arc will have.