Wow...where to start? First off let me say DO NOT be disuaded by the price....there is a LOT of material here and if you just want the capsule review here it is. Buy it- 4 out of 5 stars- some really well done crunch and fluff with just some minor nagging execution issues. Now for those who are staying along for the ride, please keep reading.
The Guide to Cthonia features art that enhances the feeling of the setting which I'm going to label Birthright meets Points of Light. This is pseudo-medieval western european done well -with suspicious peasants who trust the 'miracles' of divinie magic but persecute the 'godless warlocks' who practice arcane magicks.
There are sections on incorporating the various classes and races into this rich world. Among these is the new noble class which I found IMMENSELY entertaining. There are new paragon paths and epic destinies which show a decent command of 4th edition structure. There are some minor balance/technical issues with these sections but that seems to be par for the course for 3rd party publishers and I don't count it too heavily against the Alea group.
There is a highly useful character background section and those who have been lamenting the lack of role-playing fodder in 4th edition will gobble this chapter up.
There are feats, an almanac, a new pantheon, and more! Like I said, I don't want to reveal all the tricks APG has up their sleeves but this is a very solid product and I for one WILL be buying the next in the series.
[4 of 5 Stars!]