I figured it was time to make this, so here’s 

-the musical score is fantastic in all of them, even the weaker songs are still great to listen to. see here, here and here
-staging for the musicals gets continuously better with each one, and the third musical looks and sounds fantastic.
-Along with staging, the costume design is pretty spot on with the anime/manga.
-the plots follow certain manga plots while also keeping to their own stories
*the first musical involves a cursed flute that can capture ghosts, and the second two shinigami who just didn’t want to die alone.
-the third msuical makes Madame Red’s death more heartbreaking with a funeral duet ft her and Ciel.
-there are musical exclusive characters that are really interesting.
-Yuya Matushita is a total dork as Sebastian, and really gets into his role
-Ciel changes in every musical, and they chose younger kids for him which works really well.
-The cast is very talented and have great chemistry together
-every single cast member is a giant dork when they are together and it’s hilarious to watch
-Ciel and Sebastian get really cool duets together 
-Sebastian serenades the undertaker with a sexy love song
-Grell tries to seduce Sebastian with song
-William sings about the rules, and the entire shinigmai dispatch sings a freaking techno number
-the plots go from ridiculous to heartbreaking sad, and are just great to watch.

you can watch the first two subbed
HERE (first musical: That Butler, Friendship)
HERE (second musical(in parts): the Most Beautiful Death in the World)

the third musical, Lycoris That Blazes the Earth, isnt subbed, but you can find it HERE

there are also backstage snipets that arent subbed, but are super funny. 
first musical
second musical (in parts)
third musical

“Off to a great start with mdnaskin products with my partners Mr. Matushita and Mr. Nakajima. #wehavemanydreams #mdnaskin #mtg” -Madonna

Love for the fact

that Yuya Matushita singed Kuroshitsuji II Ending song “Bird” and the lyrics goes like: 

We, like the flowers and the trees, are pitiful, 
for we can only extend upward towards the sky. 
We realize this when we look down once in a while, 
but then again we look back up.

You look so sad in your sleep, 
as if you are having a nightmare. 
I'm right here, right by your side, 
and I'm not going anywhere anymore. 
How do I live without you?

Everyone looks at the sky. 
They look up, and again look back down, 
and they lament because they are unable 
to find that blue sky they once saw in the past.

Switching between being free and being selfish, 
we have lived this far. 
Under this night sky without even a single star, 
unable to see my destination, I simply wander about.

There hasn't been anything scary at all, 
just that there's nothing for me to protect. 
Be it tomorrow or 10 years from now on, 
I'm scared of what will happen then. 
I need huggin' my sweet heart.

Everyone weeps at the sky. 
They reach out their hands, and start dreaming, 
and they will forever protect 
that blue sky they once saw in the past.

Although there are figures soaring in the sky, 
I no longer yearn for that kind of freedom. 
Nobody is truly free; 
that is not true freedom, 
simply that there are no roads in the sky.

This midair space, otherwise known as "you", 
oh please lock me in. 
I'm not going anywhere anymore. 
Please don't go anywhere anymore.

In the middle of the sky, 
everyone is locked inside this cage called "freedom". 
All I need is you by my side, 
and then in this sky I'll have no more need for wings.

and of course the lyrics describes Sebastian and Ciel’s relationship. 

Yuya Matsushita is also Sebastian Michaelis in Kuromyu Musical