This pdf is 10 pages long, 1 page front cover, 1 page editorial, 1 page SRD and 2 pages ads. That leaves 5 pages of content.

The content starts with an aptly-written, short introduction to the matter at hand, the tome of Merenal. 4 new spells from this ancient repository are introduced:

-Ley Siphon (draw strength from the land)
-Blinding ray (blind enemies, unfortunately features an editing glitch: a missing "the" or "a")
-Odic Aura (Aura that makes it possible to either heal your allies or damage enemies via touch - for the level of the spell [Sor/Wiz, Brd 6, clr, drd 5], this spell unfortunately heals not enough/does not do enough damage - 1d6+Con-mod is a joke for this level. It's called aura, but the range of the aura does not seem to have a range of more than touch. You can use the spell twice per round, but no type of action is given for the usage of the aura.)
-Form of Quintessence (cool high-level spell, enables you to walk though enemies and living matter, optionally dealing damage and ignoring some detrimental effects)

We also get 6 new magic items, all featuring means of construction, aura, etc.:

-Primeval Staff (staff with some nice spells, fluff is rather generic, though)
-Varelium Sword (a sword that draws from the power of the land)
-Varelium Buckler (a buckler that draws from the land and can negate magic missiles)
-Ley Compass (A compass to find concentrations of magic - cool idea, but unfortunately no range for the compass is given - if it has unlimited range, it might severely unhinge e.g. investigation-style campaigns)
-Portable Outpost (an item that makes an outpost for you)
-Rod of the Ancients (Rod that helps you identify items)

We also get 6 new feats:

-Arcane Talent (lets you cast 0-lvl arcane spell)
-Healing Burst (Good idea, lacking execution: Sacrifice spell-slots to gain temporary hit points, nice for arcane casters, but will become useless at the higher levels and is only of limited use in the lower levels due to the amount of damage taken/the 1:1 exchange-rate of spell-slots: hit points)
-Improved Crafting (craft wondrous items faster - I don't know about balancing this one and frankly don't want to crunch the numbers)
-Rush of Insight (sacrifice spell-slots to gain insight-bonuses to attack - cool for Gishs)
-Single Focus (you need only one focus to cast spells)
-Savant (Treat all knowledge skills as class skills, gain bonus on knowledge skills you learned)

Finally, we get the5-lvl-Ancient-PrC. (d6, 4+INT skills, bad BAB, good will save) The class touches upon the connection to the ancients via the tome of Merenal, granting ability boosts, detect magic, changing the appearance of the character towards the Isten and having a cool capstone ability. This class is my favorite part of the book.

Conclusion:

This is the first venture of the "Secrets of..."-series that features several new crunchy bits linked by an RP-element, in this case, the Tome of Merenal. I personally think this is a great way to expand the scope of the series. The artwork is ok for the price.

However, this pdf unfortunately left me rather underwhelmed, especially in contrast to the other excellent books by Rite Publishing: The introduction to the tome, usually written IC in Rite books, felt a bit generic and left me not too impressed or inspired. The editing glitch in one of the spells could have been avoided. The aura spell is useless as written. The magic items and feats felt underpowered to me: I wouldn't take any of them, apart from "Savant" (Great for Investigation campaigns) and "Rush of Insight" (Nice for Gish). I am a bit weary of "Improved Crafting", as a feat like that _might_ (I haven't crunched the numbers) upset the balance of a campaign. While avoiding power-creep is a noble goal, I can't see my players taking these feats.

I already mentioned my problem with the Ley Compass and the magic items, especially when e.g. compared to 30 Unique Magical Blades, they all felt rather bland to me.
The Ancient PrC was nice, though.

So, what's my conclusion?

Unfortunately, this pdf did not impress me - while the price is low, this pdf falls awfully short of the excellent quality Rite Publishing has set for itself. Due to the glitches, the balancing problems and the fact that it just didn't inspire me at all to implement its components into my campaign, I'll rate this 2 stars and hope that this part of the series will improve in further installments.