Background:

Well, if you read my review on Code Geass R2, you know i loved Code Geass, i think it's an amazing show, that wrapped up really nicely, with excellent animation backed up with great writing

When i realized there was a "sort-of" sequel movie (which is this one), i was pretty skeptical, as the consensus I've seen is "It's not needed, the show already wrapped up".

"When you're going to watch this movie, remember that Shirley didn't die"

This is your last spoiler warning.

Animation:

It is beautiful, in a different way.

Since Sunrise have steadily improved their animation each and every year since Code Geass ended, they came up with A LOT of ways to make the animation even better, incorporating CGI, with improved sound design, the new armors that are layered with existing Knightmares look BEAUTIFUL (although bulky)

Sunrise turned Code Geass into (almost) Gundam and it worked spectacularly.
Another thing worth noting is "The World Of C" is also a highlight for the animation.

Characters:

All of the characters retain their personality, although they aren't NEARLY as good the original, it's very refreshing to see them back again

Not just the old, but the new characters are also pretty well written (even if they feel short)

Let's start with actually, C.C first:
Before becoming back as the ally of Lelouch's, she takes care of the initial lifeless husk of him, and it's clear that without Lelouch('s consciousness in his actual body), it would be very hard to combat Zilkhstan.

She also helps Lelouch with everything, and tries her best to take care for him despite his baby-like state.

Next is Lelouch:
As said before, he was a lifeless husk that requires the same caring methods like caring a 2-year-old infant (this might sound harsh but it isn't)

After he got resurrected, he is still the same amazingly confident and intelligent-minded person, he still has emotions and care for people he loves most (Especially Nunnally right at the end), and the best thing is: He doesn't overuse people like pawns anymore, as it seems like he repented for his sins because of Geass.

Even with Lelouch, that still doesn't mean an easy win against Zilkhstan, and that's what i like about him in this movie.

It is also where Shamna, the main villain of this movie comes along, She isn't as good as, say, Schneizel, but unique nonetheless, her Geass is extremely unique: reversing time, it means that she could retain her current memories, in a different state of time, which is pretty cool, and also serves as a great plot hill that Lelouch has to overcome and climb.

I do see a lot more potential on Shamna's characterization though, as her Geass is interesting.

The rest of the characters, old or new, are still compelling.

Suzaku becoming Zero means that he will be a major disadvantage if a terrorist attack happens (since he doesn't have Geass powers, aside from being possessed by Lelouch), he even gets tortured and beat up A LOT after being captured in Zilkhstan, and despite him hating Lelouch for his sins, he still changed his mind because living without him is hard.

Kallen is now on Suzaku's side, and Jeremiah is good too.

Story:

It's sad that the story isn't as good as the originals, but I can forgive it.

the pacing is still fast and bombastic as the old, but with newer plot points to make it stand out a bit.

I like the ending to this movie, as C.C reunites with Lelouch once again with the alias "L.L" .

I understand that this movie is more of a "Fanservice" (the literal word) movie rather than a movie that tells a coherent story, and as I mentioned before, people can find this "unnecessary". Nevertheless, i still enjoyed it.

Overall opinions

If you want to see more Lelouch doing his outsmart-y plays like he did in the original, then go ahead.