People who criticize Gundarsson's rune books too harshly should keep one thing in mind. The intended audience for _Teutonic Magic_ is not academia, SCA re-enactors, or role-players: the book was actually written by a modern follower of Norse paganism, for others like him.
From that perspective, I'm not exaggerating when I call this book a classic. Gundarsson has a doctorate in Germanic studies from Cambridge; he knows MUCH more about the rune poems, the Eddas, and other period texts than a typical "New Age" author would. He also writes vividly and fluently; the chapter on ritual poetry is a must-read for any Norse pagan who wants to compose his own. Finally, he debunks some popular misconceptions about Norse magic and mythology--enough to show a genuine interest in the facts, even though he does not always get them right.
Are there glaring errors in this book? A few (which Gundarsson later told me he would have corrected in a second edition). Is it meant to re-create ancient practices exactly? No; even matter-of-fact scholars can't do that. Does it show obvious influence from some non-Germanic magical traditions? Sometimes. (Associating each rune with a crystal? Come on!) Despite those flaws, however, _Teutonic Magic_ is worth adding to any serious Norse pagan's library.