Fanfic Willbyr's review
For me, CoaEG started shaky, got better, nearly crashed and burned during the Dreamlands chapters, then recovered well enough to merit reading to the not-ending. The final chapter (see the rec) brings the story to an appropriate conclusion, tying up the plot ends left dangling since '04 while bringing new levels of darkness to the setting. It's one of the granddaddies of NGE fanfiction, and that practically makes it a must-read, but of the Mythos/Eva fics listed on the rec page, it's the weakest overall in multiple ways.
Fanfic Unhappy's review
The Dreamlands sequences were horrible, and felt completely out of place. One moment everyone is perfectly in character, and then people go to sleep and every character is a Possession Sue. Skip them if you want to read this. In fact, don't read this. The excellent buildup in the early chapters just isn't worth the dissapointment you get as you read on.
Fanfic Tacitus' review
It is simply remarkable how well the Cthulhu Mythos meshes with Evangelion in terms of theme and tone. Cosmic horrors, paranoia, dangerous knowledge and fortunate ignorance, twisted bloodlines, forbidden and corrosive technology, insanity... It's such an obvious crossover I'm surprised it wasn't done in the source material.
Fanfic A detailed look into both universes
TL;DR - Explores both universes in great detail. Fleshed out side characters & OCs. Recommended for Lovecraft fans that appreciate his whole universe (read: Dreamlands) and not just the body & cosmic horror elements.
Having invested in both the Mythos & the NGE lore, the story rolled pretty smoothly. Some not familiar with Lovecraft's body of work might feel underwhelmed with the Dreamlands arc, due to switching to high-fantasy & space-opera settings, but I believed that the author had Shown Their Work. Shinji's Training from Hell over lucid dreaming in the Dreamlands with Asuka as a Drill Sergeant Nasty really deviated from the traditional "lovecraftian" genre and might seem narmy. The battles against the Angels are very creative (especially Uriel & Hastur), as almost all except the first are creatures from the Mythos lore.
The strongest point for me was the fleshing out of the bridge trio (Maya, Aoba, Hyuga) and their side stories. The slice of life episodes with them interacting with the pilots, Maya's crush with Ritsuko, the beach episode that turned out as a plot point and Hyuga's dilemma between Misato and an OC jazz singer really gave them the spotlight they deserved. Not to mention the adding another OC as a pilot, later in the story. Also the school trio (Toji, Kensuke, Hikari) takes the spotlight and even becomes critical to the plot in the Yellow King chapter & the Dreamlands.
Evangelion fans might crack a grin with almost every chapter ending with Gendo & Fuyuzuki's "all according to scenario" cryptic conversations, despite the Mood Whiplash on a meta level.
On a narrative level, many milestones of the original series are kept and explored further, as well as some in-universe technical issues (such as building batteries for the Units), but the story deviates a lot from the source material and goes Off the Rails.
I highly recommend it.