I have always been a person who favored rules over fluff in roleplaying games, until recently. I think with Bethorm I was actually hoping for more of the Tekumel back ground than I got. I was wanting to get into MAR Barkers works, but this is book is not a great resource for those not already familiar with The Empire of the Petal throne. You almost need to dredge up some old books to get the source material to drive stories in Bethorm.
That this book tackles is a rules system with an extensive set of magic and creature rules that are setting specific. I say that not as a bad thing, especially for Tekumel, which has seemed to have more system free sources. This gives a crunchier setting for adventures in that world.
My general impressions are the book is very content heavy per page. The material is packed on to each page. This has come with at the expense of organization and layout. If anything this book reminds me of the original The Mechanoids book from Palladium, in its lay out. It can bee a bit of a challenge looking for certain information.
All in all I see this as a good book but a very niche one. The empire of the petal throne is just weird and any buyer needs to know this going into it. Folks familiar with Tekumel will enjoy it and those of us wishing to get to know Tekumel will understand its a set on a larger undertaking.