Hidden behind cuts because of spoilers, pictures and length.
Chapter Summary
So the manga is ending and we get two formidable pictures:
(My impression is that they are the real thing and not some fan art, so I post them here.)
The fight starts with Sasuke attacking Naruto with a fireball (Sasuke's "classic" opening of a fight. We don't learn how Naruto survives this: Maybe fireballs are simply childish by now, so everyone survives them.) So Sasuke, using his teleportation jutsu, attacks him from behind with his Chidori and then again from the left.
They return to the heads of the two statues in the valley of the end, and Sasuke's next attack is with Susanoo. Naruto counters this with those blacks balls (I have forgotten their name). However, they don't work against Susanoo, and Naruto finds himself with Susanoo right in front of him. Changing into the kyuubi is the only thing that can save him now, so this is what he does:
They end up in the water and we see both of them fighting in the waves:
When their fists meet, we get a backflash of Naruto (and maybe Sasuke as well), showing them as kids just some time after the murder of Sasuke's family. Sasuke sits at the lake, while Naruto walks by, they exchange grimaces, but at the last moment they exchange a smile. We got this backflash first around chapter 228, with the last panels in chapter 229. (Well, it's rather around those chapters.)
The next backflash is from their first battle at the Valley of the End, and we get Sasuke's hurtful words to Naruto about never having been close to anyone, meaning he does not know what it's like to lose a beloved person. Since then Naruto went through Jiraiya's death, so he knows what it's like to lose someone.
We get to the present. Sasuke warns Naruto that he will die soon if he slackens as he does. (Actually so far Sasuke has been the only one to attack.) Naruto shouts at him that he won't let Sasuke kill him, because he does not want him to be alone again, "his one and only best friend". He reminds Sasuke of knowing well why he chose that place for their fight.
(I chose that picture because it looks really weird. First I thought it was some kind of bird, then I realized it's Kurama.)
Using the kyuubi, Naruto builds a giant chakra ball, while Sasuke counters this with a giant chidori, using Susanoo. Their jutsus unite in a huge chakra ball, just as during their first fight in the Valley of the end, and both boys find themselves in that white world where the characters can take some time out and talk when they need it.
Chapter Discussion
It's my last review, but I plan to write something more lenghty when the manga really ends... Looking back, even though I am not very fond of those last two years / hundred chapters of the manga, I won't forget that there were times when I simply loved it and even dreamt about it. I would not have got as angry about the manga as I did if I had not liked it so much.
Artwork: I have been often frustrated with the manga, yet what never let me down about it was the art. Its quality was consistently high during all these fifteen year. While I write this, I wonder whether this might be some kind of a problem: there should have been changes in style, with Kishimoto moving on, but at the moment I am not certain whether I could distinguish a landscape from chapter 410 from a landscape now, and even though the style did not change much, it did not get boring either. There's a certain quality of the lines and of the faces, they are never as idealized as in other stories, even though Sasuke was quite pretty (yet not in every panel.) The landscapes have always been rich with ideas. And now those two "portraits" we got. The shadows are a bit too intense (as in those "crazy Uchiha pictures"), but else, they are really great, and I think they were drawn by the artist, not by fans. They convey a certain liberty of style which only the artist himself can achieve because he does not have to worry about getting as close as possible to the original: he is the original.
Second fight in the Valley of the End: After the last chapter I expected a chapter with a lot of fighting, and in some way I was happy about it, because I did not want to go into the deep stuff. I was looking into having to explain what is going on, but actually there is not much to explain. They don't use any tricks (or we don't learn about any tricks), they just attack each other with their strongest jutsus. There have been better fights, fights where people did use tricks: Sasuke against Deidara, Sasuke against Itachi, Sasuke against Danzou, Naruto against Pain. Maybe even during their fight against Obito there were some intelligent tricks, but this fight took so long that I don't remember them. Even when they fought Kaguya they used some tricks. But maybe this will change when their time-out in that white land without background is over.
Emotionally there's something weird about that fight. The first fight in the valley of the end was filled with hot emotions: Naruto wanted Sasuke to stay in Konoha, Sasuke wanted to kill Naruto because he thought that this might give him the Mangekyou Sharingan and because he did not want to go back to Konoha but he wanted to leave and train with Orochimaru. None of this was very sane, but in some way it was understandable, and it also makes sense that Sasuke had lost his sense because of his despair about not being able to defeat Itachi. Sasuke wanting to kill Naruto now seems rather "cold", the reasons he gives are just confusing instead of in some way understandable but still wrong.
Backflashes: We get a couple of backflashes of scenes we already know. I don't mind backflashes per se; Naruto has had some great ones - the whole volume 25 mainly consisted of backflashes. But these were new backflashes at the time, which gave us some new information. Maybe I should be more patient with this rehashing of old backflashes: after all, there's kids reading the manga who have not read the previous 694 chapters, so it's necessary to give them some information and to get them interested in the story. Still, with only five more chapters, one would think that Kishimoto is a bit more economic with space.
Now concerning the boys' friendship: It's true that it mostly consists of a few months when they were actually members of Team 7 and interacted with each other, and we don't get many exciting backflashing about the two of them (plus Sakura) sitting together and chatting during a break. Instead we get glimpses of them noticing each other and putting more meaning into those moments than is realistic. It is as if they were fantasizing about each other, or at least Naruto about Sasuke, giving that moment at the lake some huge meaning. But actually, it's only through real interaction that such a moment can gain meaning in hindsight, else it's healthier to move on. (But then the manga has never been about what is healthy).
699 or 700? My interpretation is that we will get 700 chapters. I just does not make sense to end with chapter 699. So my interpretation of the announcement is that when it says "five chapters" the present one is not included.
shocking ending? Actually I have difficulties imagining a shocking ending. Well, of course I can: Sasuke really killing Naruto, or the other way round, or both of them getting killed. I just don't think that this will happen. Sasuke will marry Sakura, Naruto will marry Hinata, they'll be friends again, Sasuke will refound his clan, Naruto will become Hokage, though maybe only after Kakashi retires, there'll be peace among the ninja countries - I cannot imagine anything else. A tragic ending would run against the central message of the manga, namely that true friendship will overcome all obstacles.
Concerning the things that need to be resolved: Well, I fear there won't be any discussion of the Uchiha massacre any more. It's now all about what Itachi did or not did, sacrificing himself, acting all alone - but not whether what he did was good or evil. I fear that just like a lot of fans Kishimoto thinks that what Itachi did was the right thing, as he prevented a rebellion. On the other hand, I would like to learn a bit more about Sasuke's and Itachi's parents, who did not fight back when Itachi was killing them and who warned Sasuke against choosing Itachi's path. It would not need more than one chapter to learn a bit more about them.
Also there's still a lose end about Karin. Apparently she's from the Uzumaki clan. What would Naruto say when he learns this? On the other hand, I don't think it's very important now.
Other lose ends... Yamato and Anko. I guess they will be saved with the other ninja when the Infinite Tsukuyomi is resolved. And then Sasuke needs to get the Rinnegan in both eyes. I am quite optimistic about this last point, and maybe this will give him some new insights.
Not much more comes to my mind, but maybe you have more ideas. All in all I could have done without a fight Sasuke versus Naruto, and it feels a bit artificial to me, but maybe the fans for whom the most important point of the manga is that Naruto gets finally stronger than Sasuke needed some kind of reward for their patience. (I think they missed the point of the manga. It's not about Naruto getting stronger than Sasuke but about both of them becoming friends.)