Some fantastic Spells that really expand the elemental magic spell list avalible to players. Also love the Elemental Magic Item "Magma Mantle" hoping for a follow on book.
Happy to say that the follow-on book exists! The Heroes Handbook for 5th Edition includes the Deep Magic series and much more.
http://www.drivethrurpg.com/product/236914/Midgard-Heroes-Handbook-for-5th-Edition