Simply put, Platinum End is a story about a boy who commits suicide, but is saved by an angel so that he may participate in a battle royale to become God.

Disclaimer: Platinum End takes a very cynical view on the concept of God. If you love listening to Pastor Dave preach every Sunday, I would not recommend this to you.

Tl;dr
Platinum End is philosophical and presents interesting questions on the role of God, but suffers from a lack of character depth. However, I thought it was interesting and I think you should give it a chance and read with the role of God in mind.

The story is written by Tsugumi Ohba, the critically acclaimed writer of Death Note and Bakuman. In terms of story telling, Platinum End does not reach the intimacy that Death Note and Bakuman.
Platinum End is set in modern society, so there is little world building. Thus, it heavily relies on the characters for most of its story. There is a great emphasis on specifically human psychology and their outlook on life. Topics such as greed, depression, cynicism, etc. are used as a means to question the role of God. Many of them come off as simple and one-dimensional, but not out of place.
The story heavily relies on the dialogue between these characters who have all decided to take their life and are chosen because of their dissatisfaction with the world. The core theme that this manga centers on is the role of God. How should God act in the face of cruelty and injustice? Should God intervene to make humans happy? And specifically, What is God?

The art is by Takeshi Obata, the same artist that partnered with Ohba on Death Note and Bakuman. If you love his art style, there is more of it here! The art style is definitely not as radical as Death Note nor perky like Bakuman. It is more somber and blurred compared to his previous works.

From here on out, I'm going to take a more polar stance on this manga.
Personally, I found myself realizing that the scope of this manga is too big for its own good. That's not to say that it's terrible.
First, characters in this manga are shallow. But I believe this was intentional and too much of it would take away from the core themes that Ohba was trying to establish.
Second, this manga handles its main character in a somewhat unorthodox way. It establishes Mirai as a depressed main character, but he rapidly turns into a messiah character. I found him to be somewhat unrelatable toward the end. A similar thing happens with the main heroine and I believe that most readers would loose interest because of it.
Third, the angels literally do next to nothing for the story other than being a plot device. There is little to no character building for them which I believe is a missed opportunity.

Overall, I thought it was a fun read and the somewhat open-ended? ending was interesting.