Thinking of buying this supplement next so looking for a few pointers...
Is there a lot of supporting text in here, backgrounds, ideas and pseudo historical hedge traditions
Or
Is it another one of those books with 20 new types of magic to try and grasp (such as the mysteries) - which in my case will mean it goes largely unused.
Short answer : yes. A good description if you change the "or" to an "and".
Sort of.
Hedge Magic Revised details six fairly complete magical traditions (I say fairly because the Elementalist and Nightwalker traditions do require some customization before they can be used) each with its own unique flavour, background and a number of story seeds describing suggested interactions with the OoH.
While there are integrations (ala Ancient Magic) than can be used to improve Hermetic Magic, but the emphasis is on having highlighting alternate magical traditions for use as enemies, allies or PCs.
Salvete, Sodales!
My recommendation: Get the book. - Ok, I had been waiting for it since they published the core book, I love the learned magicians (basically this editions version of the 4th ed. "Natural magicians", even though they have changed dramatically), so I might not be the most neutral person in this. But I'll try to control myself:
As Gremlin44 mentioned, they have included six magical traditions (Elementalists, Folk Witches, Gruagachan, Learned Magicians, Nightwalkers and Vitkir). I won't go into detail about their specific characterisation, but you will find older threads in this forum which are pretty thoroug. You can use members of each tradition in nearly every function in your saga (My hedgie in the AdFons saga on the board occuoies my magus spot), even though it is no surprise that using these guys as magical main characters leads to open questions from time to time (compare the space they get in one book of about 140 pages for six of them in comparison to the number of pages occupied with the options to hermetic magi), but they are playable, and the mechanics aren't really new, so that getting used to the traditions' specific rules isn't much of a problem. It was intended that even the mightiest representatives of these traditions fall short of the power level that hermetic magi of comparable experience get, but there are enoug unique abilities that might offset this, as long as you don't plan an open magical battle. Of course, there was Michelle's hint recently hinted that they are planning to publish "Rival Magic" this year, and David's comments about the subject suggest that it is a good alternative, so if you are short on money I'd wait and decide after that has been published.
But if you have enough money to spend, get 'Hedge Magic (re)".
Vale,
Alexios ex Miscellanea
I didn't really like HMRE. I think the mechanics are too complex for NPC characters, and often too vague and SG-dependent for PC characters.
That said, there are six rather well-described traditions, plus a few smaller alternate-traditions that use the same mechanics but with a different background. So I think it would fit what you want fairly well, although of course some traditions are less well described than others.
So to a very great extent then to make use of this supplement, like so many others, one has to learn new magic systems...
Do I stand alone in wanting more to be incorporated into the basics? I find this approach to expansion grim in the extreme. Why cannot more things be incorporated into default rules by adding a simple list of ammendments for particular groups rather than constantly having to learn more entirely different rule subsets?
It would be boring...
Boredom was born on the day of uniformity. 
Yes and no. The problem is that Hermetic Magic and nonHermetic Magic work in different ways, and making them use the same Arts et al would be odd (This guideline only works for X type of magic user) and confusing (actually, only Y magus can read this book usefully). The new ones do all use the same basic structure (Art/Method + Form/Type), at least, unlike the 3rd and 4th edition ones and so are easy to understand and follow. The Elementalism chapter has three different types of elementalist all using the same Arts with different emphases and I found it very confusing to follow.
I stopped being excited by rules about 20 years ago, by which time I must have played at least a dozen systems.
Stories are fun, rules suck. Some more than others, and you need em, but the simpler the better.
In my experience of writing complexity is very easy to achieve. You just have to add more. The true skill is in crafting something simple and elegant. Ars had that once upon a time and seems to have completely given up on the idea.
The information is there to do just that, Restless Kaiser. The neat bit (in my eyes) is that each of the "traditions" has something they can do that Hermetic Mages can't. So while a Real Mage can crush any of average members of same traditions, there is good reason not to do so. Convincing a Natural Magician to help in the lab would be a pearl of great price. Perhaps too much. A lot of stories in what a player will do to get this great resource, coupled with what they will do to protect themselves from betrayal. Then there's the rules to incorporate the "alien magic" into Hermetic Theory. As written, each tradition can be incorporated, but not perfectly. For example, you can learn how Natural Magicians make "very quick" magic items. But that doesn't touch the "luck control" thing they have going on. Can that be learned? Is it possible to incorporate into Hermetic Theory? Canon doesn't say......
If you really don't like the idea of introducing alternative magic systems into your game I doubt it'll change your mind, but the actual mechanics used for representing the traditions' powers are actually fairly simple.
Elementalists: Use a Noun and Verb system, but without using spells their powers more similar to the Goetic or Fabulous Arts. In any case, their powers are clearly defined in the text.
Folk Witches: Most of their powers rely on standard Supernatural Abilities although some of the applications are a bit unusual. Their lab work in pretty similar to the hermetic model too.
Gruagachan: Use a Noun and Verb system very similar to the hermetic one, using pretty much the same parameters for determining the RDT. Their lab work is extremely simple and follows the hermetic model.
Learned Magicians: Use a Noun and Verb system similar to the hermetic model. Their lab work is a bit more sophisticated than the other hedgies, but still rudimentary by hermetic standards.
Nightwalkers: Most of their powers require no rolls whatsoever.
Vitkir: Uses Accelerated Abilities with clearly defined EFs. Choosing the Method and Target (if applicable) can be a bit confusing at first, but its child's play once you get the hang of it.
Agree with Gremlin here. I found this no big hassle once you tinker around with the system.
IMO this is the best book for 5th edition so far. Only beaten by aret and acadme if you like non-magic stuff.
My main concern was that some of the traditions do not fit well with my own vision of "whart should have been done" here, but that is a highly personal stuff. For me the "weaker" ones are the witches (too much stuff dumped into a single ability) and natural magicians (and cunning folk) requiring no vis (I am more of an "alchemist" approach here). Gruagachan and Vitki are just AMAZING. I never got the hang of the elementalists, but that is because I was hoping to see people that could cast CrIg spells at a certain cost (like what Flambeau or Guernicus could have been before being taught hermetic magic, in a sense), and got something totally different out of the chapter. If you like weaker magic practioners, I would highly advise this supplement. We are about to use vitkir, gruagachan, natural magicians (well, cunning folk) and witches IMS, so yes, we are giving this book a heavy use, even if most will be NPCs that hang around the Isle of Mann.
Cheers,
Xavi
Hi,
Ah! I get excited by great rules. For me, rules are good to the extent that they model what is supposed to be going while being usable, but great rules do this while being dead simple, even elegant. Great rules are hard to come by.
Anyway,
Ken
No, you're not alone. If this is a game about Hermetic magic, why can't we get more interesting supplements about ... Hermetic magic? 
This is why I was so glad to see Magi of Hermes. 
It doesn't expand anything, but it uses what's there.