I've just started, but it's very interesting so far! The worldbuilding is great, and I really like the idea of having two elements. The author also does a great job of introducing new characters.
There are grammar and tense errors, but in terms of helping the reader visualize what's going on, the writing quality is better than 95% of what's on this site.
I'm giving it a 4.6, but with a good copy editor it would easily go up to a 5.