There's A Good Show Hiding In Here...
This review will cover the anime only, without consideration of the visual novel.
11eyes is one of those frustrating shows that could be great, if only there weren't so much holding it back.
There is an amazing story to be found here. The characters are likeable enough to make you care enough to follow them. They each have something going on in their lives that is tragic, or touching. There is some amazing world-building elements, and the plot twists are difficult to see coming. Unfortunately, while the show has very good points, they are bogged down by clumsy execution.
Likeable as the characters are, they don't have quite enough depth to carry the story. Initially Kakeru's devotion to Yuka is endearing, but towards the end, he comes across as too single-minded. Yuka's devotion to Kakeru turning into a creepy obsession is shown via one too many scenes of her wandering in on Kakeru and Misuzu in a Not What It Looks Like
situation. Yukiko's backstory is given via her telling Takahisa with little prelude. Takahisa's backstory is also given in an awkwardly-placed flashback, and his sudden madness over a certain thing that happens and how Yukiko has to deal with it is not given a lot of time to develop. What should have been a couple of the most heartbreaking scenes instead don't leave much emotional impact because of how rushed into or out of they are. Misuzu's character arc is developed a little bit better, but even her part of the story seems a bit lacking; her past could have been delved into a bit more.
The animation is basic, only doing what it needs to do and nothing more. The character designs are very typical.
There is some gratuitous fanservice that feels out of place and grates very quickly, and there are some comic relief characters who might as well not be there.
With that said, the music, while not memorable on its own, does do its job very well, setting the proper mood for each scene very gracefully. The openings and endings sound fantastic (unfortunately, as far as watching them goes they are as basic-looking as the rest of the show.)
All told, while it is an anime worth seeing at least once, it is a bit sad because it is clear there is a great series hiding in here somewhere. All the pieces are there; it just didn't quite have the storytelling chops to be able to pull them off with the grace and finesse they needed.