This book has great ideas, but has numerous issues which I think the author is in the process of growing out of.
The switching back and forth from fantasy to sci-fi is a very fun idea. The worlds are interesting, but simultaneously too deeply described, and quite simple. If you think of playing World of Warcraft from a space station, you'd have it set decently.
The characters are pretty typical, except for what the main character is put through.
An editor is desperately needed. There are lots of typos, and places that could just use smoothing out. It also needed to be a bit longer, because the punch lines in the last 20 pages are rather vexing, and made it feel like a prequel.
So why a 4/5? Because it is enjoyable. I'll probably read the rest of the series at some point. Also, the author's skill seemed to improve further into the book. It is a unique idea, it is fun, and easy to read. I feel like if the author was to rewrite the book in hindsight, it could become a masterpiece.