The style is very much in the feel of the old B/X books. The text and most of the art is by Doolan himself, so kudos in that regard.
We start off with some class variants. The obvious parallel here is when the UA expanded the classes demi-humans could take but it also fills a niche. Not all elves use magic, not all dwarves swing an axe. While we can see some of this in ACKs, this has a tighter feel with the B/X design. We get two new races, the Half-elf and the Half-orc and two new classes, the Barbarian and the Martialist.
There are some rule additions including various to hit bonuses, rules for Followers and the Mass Combat rules.
Mass Combat is interesting since it is a backwards evolution of what D&D took from Chainmail.
On the down side I did not see a declaration of open content. The OGL is there, but not the copyright for this book or how much open.
Also while the book feels packed it is only 17 pages total or about 14 pages of text. I am of two minds on this. First the book does feel packed, so a lot was crammed into these 14 pages of text. On the otherhand is $3 too much for 14 pages?
In the end I judged the price fair, but I would have liked to have seen some more. Some special spells for the Dwarf Priest and the Elf Sorcerer would have been nice.
Who should buy this?
If you are a big B/X fan (like me) then there is a lot of value here for your buck. If you play any of the "Basic Era" games then there are things you could use here.
I think there is worth while in identifying some spells from various "Basic" sources that might work well with the new classes. Books such as Magical Theorems & Dark Pacts and my own The Witch.
You can find Tom on the web at http://wishfulgaming.blogspot.com/