This pdf is 13 pages long, 1 page front cover, 1 page editorial/ToC, 1 page SRD.

That leaves 10 pages of gaming material which are, as I’ve come to expect of Spes Magna Games, well-edited and printer-friendly.

The idea of Ars Metamagica is, that one abolishes metamagic feats and replaces them with a new system that actually gives metamagic some game time and makes players use it:

Modifying spells is now done via a kind of caster level check that depends on the metamagic art you apply to a certain spell. If you fail the check, you have might experience some repercussions, depending on how bad you failed: 4 or lesser means that the spell works without metamagic, 5-9 gives you temporary ability damage and a failure of more than 10 fatigues/exhausts you and might even deal subdual damage, if repeated.
Every Caster gets a selection of slots every day called “Metamagic palette”.

If e.g. you have a palette of 5, you could choose a metamagic art with a value of +3 and +2. Or 5 arts with a value of +1.
You can also leave slots on your palette open and meditate 1 minute per +1 to fill them semi-spontaneously.

Both preparing and spontaneous casters are addressed and the pdf also takes the metamagic feats from the APG into account. The pdf takes several factors into account and offers revised version of the bard spell Arcane Concordance, a new universal Metamagic rod, Healing Domain’s Healer’s Blessing, Loremaster feat requirements, Magician’s Metamagic Mastery, the feats for Heightened Spell, Reach Spell, Spell perfection and Preferred Spell, the Sorceror’s Arcane Bloodline and the Wizard’s Universalist School.
We also get 5 new feats to be used with this system as well as two new traits.

Conclusion:
This file has been exceedingly hard for me to rate due to several reasons. First of all, I don’t like the standard metamagic system, as it rarely gets used by players and is rather cumbersome. I’m also a fan of magic that may take a toll on one’s body, as reflected in years of house-ruling battlemagic and the like. However, somehow this pdf did not make me jump up and scream “Yes, that’s it!” I was thinking quite hard why that was the case and found the answers: The first one being that, while taking many special metamagic-using abilities into account, it does not provide guidelines for future additions. The second would be that, while comprehensive and well-written, it is not as comprehensive and well-written as some other releases by Spes Magna Games: It took me 3 pages to get the general idea of the system and while the presentation is concise, I think showing the table with all the modifiers before explaining the basic premise of the system is a needlessly complicated way to lead one into the new system.

That being said, you do get a, at least in my opinion, better metamagic system than the one in the standard rules for less than a bus fare.
Another major plus is the excessive support of the APG.

In the end, I’ll settle for a solid 4 stars for anyone who is interested. For all the people who abhor the current metamagic spellcasting system, but want to keep most of the rules intact, check this out – for you, this is a 5 star-file.