Pros:

~The music choice. The music choice. Aaaand, The music choice. This is a perfect blend of such different genres of music. 

~The concert is most definitely the best concert modification on this site. (The concert music on this mod is far better that the music on Devoc's individual concert mod in my opinion.) 

~Even so, Devoc made very high quality pictures that enhances the Dark Carnival campaign enough to bring the player to another world.

~Zombat music is pretty sweet. I love how you chose Slayer music for...the horde slayer. Jeff Hanneman and Kerry King cracking of some crazy riffs while you shred zombies. Actually, the zombat music is F****** awesome. I would love it if you could release the zombat music on its own. (RIP Jeff Hanneman.)

~I'm surprised you managed to replace the Passing's radio music. I don't think I ever seen that before.

~It's Hatsune Miku. It's Vocaloid. Like it or leave it. I happen to love it.

Cons:

~Every track is cut, for obvious reasons that I would guess is unavoidable. 

~I can see some people being upset at how the zombat music is unrelated to Vocaloid and Miku.

~This mod contains quite a lot of hard rock and metal, which i can guess is unpopular to Hatsune Miku fans, not including me though. 

~If you cannot stand screaming (Yes, Hatsune Miku does scream and shout on some tracks, such as the tank music when she screams DIE!!! DIE!!! DIIIEEE!!!!!!!!), you might not like this. However, if you feel like you are mature enough, this would be an interesting download. The game itself is rated M, so I would guess this would not be much of an issue.

Conclusion:

How do I start this. I've been a vocaloid fan since 2009, and I picked up Left 4 Dead 2 about a year and a half ago and I'm still in love with it. I've also been following your mods ever since this mod was version one. Killing zombies and rocking out with Hatsune Miku takes the whole Left 4 Dead experience to another level. Today I finally decide to open my mouth to express my gratitude. Thank you so much for your vocaloid mods, and I hope your future works will be just as awesome! 

PS: It would be helpful if you could post all the names of the music producers in the changelog.