I really like the base-concept of Exilium!
You can think of this as an ideology to have today, which makes it very easy to empathize with:

Imagine all the evil people you players heard of in the news: Murderers, Scammers, etc.
In Exilium these people are not themselves. They are possessed; "Shadows".

Players not knowing what they did, to deserve exile, but rather finding out while playing is also very good. If you are surprised by the character you play, that's always a plus.
Same thing with Elysium not being pre-defined. The group deciding, why Elysium is the beautiful place it is, is smart. Makes every game different.

Another bonus: Since you're not creating all of your character, but only the inside which then possesses a hull, visual character creation can be randomized.
We all know this one person, who basically play the same character in every game they play

While reading my brain is already working:
Having this in a today, mundane setting would be awesome! There's a world behind the world … Sort of like the Matrix!

So where is all of this action taking place? The second half of the book is dominated by a large setting chapter titled, “The Flame Worlds”.

Okay … I guess my Matrix analogy isn't the books intention. :-(

I would like it way more, if the group itself could decide the setting they play in.

I will definitely try running the base-idea on a generic system like FATE some day. Maybe even write a small PbtA hack for it.

I'm still wondering two things, btw:

1. How does the group stay together?
   Is it just assumed they stay together? In a setting like this I don't immediately think of asking other players for help. Unless every Shadow we hunt is a big fish …
2. Are there "classes"? If yes, which?