Fine.
Now that I've bitched about the amount of content on to the content itself:
It is by Aaron Dembski-Bowden (aka Dead Blue Clown on these boards), and while I have not read the whole PDF yet the contents seem very good. It starts with a few pages on Runes, Locating them, Integrating them, and Runecasting. This covers some ground already covered in the core rules and expands on it some. There are also some cultural stories on the origin of runes (A God Learner Speaks, An Orlanthi Speaks, etc). Then it gets on to the Runes.
Each Rune starts with a description of it from the point of view of a culture (Praxian shaman for example) and then a description of the rune and what it represents, and then a table of Runic Powers. Each rune now has 3-6 Runic Powers, and when you integrate the rune you roll to see which power you get. This replaces the Rune Powers from the Core Rules (one of the powers in the new table seems to match the one in the book. I like this variety, and some of the powers are pretty cool, some are damn useful (roll 1d12 for SR instead of d10) and some are of the +10 to Runecasting(this rune) variety.
There is a rule that allows a high level character to attune a second rune of the same type for a second power, though this is at -100% and costs 2 POW, so it will not be common.
And that is the contents of the PDF.
Now to the Art. I love it. The Death Rune on the Broo's skull is great. They are all full page paintings, and I really like them. They are NOT standard fare formulaic generic fantasy art. Kudos to Mongoose on not playing it safe on the Art. Sometimes they take flak, as in the Lankhmar cover, and sometimes it really pays off. There are a lot of people who can do fantasy 'graphic art' - by that I mean well rendered, safe, commercially viable art. Mongoose seems to go for artists with that don't fit this mold. I think there will always be some controversial art as such, but none the less: Bravo (standard excepting pig nose Trolls disclaimer here).If all the art in Magic of Glorantha is like this I am psyched. Nathan Furman you are the schizznit.
I have no Idea why there is a credit for Maps. There are none (but if there were I'm sure they would be good Keith Curtis).
None of it offends the Gloranthaphile in me. But then I was never offended by the whole Rune Integration thing, yes it changes the world but it has a very Gloranthan flavor - one could argue more than the old Battle Magic.
So, in summary, the Contents are very good. I just can't say there seems to be 5 bucks worth of them. As I mentioned in my first post I'm not sure how I feel about the scraps from published books all being sold as $5 PDF's. Sure we get access to stuff we might never have seen, but at 20 pages thinly covered with text this could have been cheaper, or maybe a freebie, or perhaps bundled with some other piece of edited out goodness. If $5 bucks isn't a big deal to you, I can easily recommend it, If you are a very budget conscious gamer I can't say that I do.
As a preview of Magic of Glorantha it has me pretty psyched for that book.