The pirate alliance arc begins with Punk Hazard, which was a nice change of pace to the overall boring fishman arc. It had its moments, with the introduction of somewhat likable characters like Kinemon, had a good introduction with the conflict against Doflamingo, which had presented itself as a charismatic character and had good scenes with good emotional value like Monet and Vergo's farewell to Doflamingo (although that can be ruined if they're shown to be alive). It featured consistency by Zoro, with him reminding Luffy how the new world requires a serious demeanor, but sadly featured Luffy with the same overall childish demeanor he had on part 1, despite all that he had been through in the Paramount arc, which would force a more serious behaviour towards the conflict they were on. Luffy also losing to Caeser the 1st time is somewhat hard to swallow even if the protagonist was taken off guard by his attack, as Caesar overall demeanor and attitude later on implies he is a total weakling to the new world average level. It also featured some moments that, while minor, had you muddling over a bit, as Sanji smoking while on Nami's body, despite the fact that he has shown to value the good health of every crew member, specially the women.
As for Dressrosa, it was an arc that had a good beginning, with the introduction of big tier characters that could make such a well-grounded arc, but failed somewhat on its execution, with such characters serving little more than aid-ins so Luffy could get the final blow against Doflamingo. Luffy's fight in the G4 against Doflamingo also loses a bit of its potential value as we later see that Luffy could have just used his King Kong Gun to make things simpler from the beginning, but decided to hide such an attack only for the sake of dragging the entire thing out and building drama to the closing up birdcage when we already knew by the somewhat predictability of the story that everything would end up in the best way possible at the end. Not to mention that it suffered from repetitions of past plot points, mainly Alabasta, with Doflamingo architecting a plan to take it up in which blame would fall upon the king's shoulder much like the King Cobra situation in Alabasta, featuring characters whose role would be also akin, like Rebeca and Vivi. It loses point on originality. Despite it, I still think that Doffy's characterization was well done in the manga, with him being consistently presented as a sadistic villain that seldom loses its cool.
So, while arcs that didn't fail hard as Fishman Island, it still isn't up to what was presented in the best arcs of part 1.
Punk Hazard - 5/10
Dressrosa - 4/10
Overall - 4.5/10