A Great read through the book head to toe, or front to back.
But a number of Major Fails exist,
1) The Ifrit, Oread, Sylph, and Undine are not true to their names, or origins; Ifrit is an other name for Efreet, Oread are a type of mountain nymph, (WoTC got this right in Fiend Folio), sylphs are Air Elementals (again WoTC got it right), and Undine are a type of water nymph.
2) The Ifrit, Oread, Sylph, and Undine feel like paizo's version of the Genasi from the Forgotten Realms Campaign Setting, and forcefully made to fit into as it's replacement since they don't most likely have rights to Forgotten Realms.
3) Again the same 4 races, have equal CR to an Aasimar and Teifling, but are weaker,i.e. no racial skill bonuses, less total resistance values (Aasimar and Teifling have Three 5 element resistance, they have One 5 element resistance), the only thing they have that Aasimar don't have is Elemental affinity which take me to the next point,
4) Elemental affinity for me is looking at the whole is equaling half its CR value as a waste, and it not class universal and acting as the Favored Class mechanic of 3.X favoring a specific class of specific type with a bonus, So I am house ruling a swap of Elemental affinity for something more appropriate for the race it stands for and that is more class universal.
5) Why are the Aasimar, Ifrit, Oread, Sylph, Undine, and Teifling of type outsider(native) when they are Mostly Human, instead of humanoid(human, Outsider X blood) where X is the outsider's race, and where outsider X blood gives you the ability to use outsider stuff, but also enables effects against that of outsiders on you i.e. bane.
Dispite these major errors, the book is great collection of monsters from previous and coming Paizo works and folklore creatures, but a double checking of the origin of the creature's name, creature types and checking Playable races of equal CR against one another would have made the book much better.
**For reference I did compare the Aasimar and Teifling against the Ifrit, Oread, Sylph, and Undine. and checked the Ifrit, Oread, Sylph, and Undine in Wikipedia.