So, the final episode of Sword Art Online: Alicization have just aired in Japan this week, and while I haven't watched all the episodes, (I still have 8 left,) I can say that this is the best season in Sword Art Online and I can definietly say that not only the animation team, but also the author have improved immensely since the first season!
Sword Art Online is one of the most popular Anime/Light Novels in Japan, but it's one of the most divisive outside of it. Some people think it's one of the best anime ever, some think it's overly overrated. Some think it's a mediocre at best with some questionable moments and bad writing... Well, I believe Sword Art Online is very flawed, but I also believe this anime is so fun!
There are many flaws in Sword Art Online, if you watched it or some videos about it you'll bound to notice them but I won't be talking about the flaws here. There are two things that this anime does completely right: Hooks and Animation! (You can replace the last one with "emotion" for the novels, because in the anime version, emotional moments are hit or miss. The books aren't animated but some of them are better than the anime.)
So, I think the best thing about Sword Art Online and the reason for the anime's popularity is the great hooks it offers. The first two episodes of the first arc are great and contain so much potential that they make you think of how good the anime must be... Until you don't see anything of that potential manifest later and you might get disappointed.
But that's the thing, expectations play a huge role on how you perceive Sword Art Online, if you knew you're watching a badly written, power-fantasy story with many Isekai elements shoved in, Sword Art Online might be actually good! When I don't take the story seriously I find that it does many things right...
What I said about the hooks/premises is present in every arc. Even the arc I didn't like at all, (Alfhiem Arc,) has a very good hook: (Kirito has to enter this new game to save his wife,) it's just that this arc had some questionable premise, bad arc villain, and is overall way lower quality than the first arc.
The trend continues for the next season as well: Phantom Bullet arc turns Sword Art Online into Star Wars, and the light sabers hooked me instantly. Calibur might be a filler arc but it's necessary breather before the next arc: Mother Rosario which is one of the best arcs in the series and in my opinion the most emotional/heart-breaking. All these arcs had a different but equally impactful premise that has a lot of potential... Until you realizes that the author didn't change and you probably won't see any of that potential, but hey, that's what imagination, fanfiction, and SAO Abridged are for! More original material means more ideas to draw enjoyment from!
I have to say that Reki Kawahara might not be one of the best writers, and his story has many flaws, but you can notice the improvement of his writing ability in every arc over the one before. (Even the second arc had a better pacing than the first in the novel version. Mother Rosario is amazing despite containing totally inaccurate medical information.)
SAO: Alicizaton takes every thing good about the story and makes it better, by isolating Kirito from the rest of the cast. Put him in a very realistic Virtual World with mystery in every corner, and give a male deuteragonist after all this wait. Alicization arc has the best themes in Sword Art Online, questions life, the humanity of AI and the difference between the real and virtual worlds. It's also the logical evolution of SAO's first arc, while taking into account everything Kirito and his friends have learned in the arcs in between!
One thing about Alicization arc though, the main story motive of the arc is that Kirito believes that AI are people too, and they shouldn't be sacrificed. The protagonists fight for the rights of AI. If you don't believe in that, the whole premise of Alicization becomes stupid.
Finally Sword Art Online: Alicization has the best animation of any anime I watched, ever! (Well, it takes the second place after Fate/Stay Night UBW.) The animation of SAO was always good, and better than most of the anime it aired with, but Alicization and its second half in particular takes the animation and makes it way better! Fitting, because the second half is titled: War of the Underworld and it does make you care about those AI fighting each other~
Finally, I want to say to those who haven't watched Sword Art Online because of its harem elements. I would say that while SAO has many of those elements, it's not a true harem series. (Kirito only loves Asuna.) Sadly, I think the harem elements are only there to "sell" and they do drag the story down a bit, but you can ignore them as you watch, because they aren't in the main parts of the story.
What I want to say, if you look past all of SAO flaws, it's a good anime and while I disagree with many of its themes, and the writing is obviously not good, it's still a very enjoyable anime. Since most of the audience care more about "fun" and not about the show being an actual masterpiece, I think SAO has the right to be that popular.