First and foremost, the Kage Summit arc gave us some great world-building. We were introduced to many of the hidden villages for the first time, and got to see their key shinobi in action while learning about each village's political stance / personality. We were set up for the War Arc fairly smoothly. We also learned about Ten Tails, Indra, and Ashura, giving us some big insight into the Uchiha/Senju dynamic.
The action was very well-written, especially the team battle dynamics (Taka vs. the Raikage's team was an excellent fight). We got to see Sasuke master his MS against high-level opponents, while also seeing some cool new fighting styles in action.
Sasuke's character development was the focal point of the arc, with his descent into darkness happening at a fairly rapid pace. I won't say I'm a huge fan of this version of Sasuke, as I much prefer his cooler demeanor during the War arc (after Sasuke had a chance to speak with Itachi and the Hokages). However, the Summit arc is a huge moment for Sasuke's character. I suppose my favorite part of his development would have to be his interaction with Naruto, where we get to see that glimmer of hope for Sasuke as he was obviously impacted strongly by Naruto's words.
However, aside from that great Naruto/Sasuke moment, I'd say that Naruto's role was the weak point of the arc. After showing so much growth during the Pain arc, Naruto came off as just awful during the Kage Summit arc, and the writing forced him into some pretty pathetic situations. From allowing himself to be beaten senseless by Karui on Sasuke's behalf, to bowing and begging the Raikage to spare Sasuke, to hyperventilating after hearing about Sasuke attacking the Summit meeting.. Naruto just looked fairly pathetic. To make matters worse, he had to deal with Sakura's mind-boggling "confession", which thankfully Naruto was able to see through.
I'd also say that the filler in-between the Kage Summit and Sasuke vs. Danzou was not needed. Killer Bee vs. Kisame was a boring fight, IMO, and wasted time, particularly since it ended with the cliche "It was a clone!" The stuff with Ao fighting the Cursed Puppet technique, and Obito wrecking Danzou's henchmen, was also filler. It just came off as a few wasted chapters.
Sasuke vs. Danzou was excellent; no complaints about that fight.