Leviathan question

As a 20-ish year old, I enjoyed it, but yes, it is intended for Middle Grade/YA.

It is intended for a Middle Grade audience as Dustin said. But you can still enjoy it as an adult. The prose is not trying to dumb itself down, the illustrations are really nice, the worldbuilding is superb. I'm 27 and I have it as a permanent fixure on my bookshelf. It's a good steampunk series.

I first read it when I was 20-ish and I quite enjoyed it. However, I'm 28 now and re-reading it can be a little dull. So, it really depends on you as a reader. It is very much a middle grade book.

I read it when I was over 25 (if I remember correctly). The setting was nice and it's still readable if you're not a teenager.