I've been running a PHB/AE mesh game in the Oathbound setting for about a year now, and there are things I like and dislike about the system. 
The biggest pro is the magic system (and really the main thing I use from teh book). Iit moves away from the irritating vancian system, which is a huge plus for me. I cant imagine playing a 3.5 wizard or sorcerer in comparison.
You essentially have a caster who can cast a certain number of spells each day, then prepares a list of spells each day. For instance, you might be able to cast 4 1st level spells, and have 4 first level prepared. So you can crank out 4 of one, 3/1, whatever combination floats your boat. This removes annoying situations where a wizard prepared a utility spell with no use.
Another feature of the magic system is the ability to weave spell slots. You can break a higher level spell down into lower level ones on a 2:1 basis. So you could convert a 4th level spell into 2 3rd level ones. You could then convert one of those 3rd into 2 2nd, etc. Additionally you can merge 3 spells of a level into one spell of a higher level. So 3 3rd level slots become a 4th.
Healing magic is a simple spell. Anyone who can cast, can heal. However, the nice feature is that healing is a bit harder than normal. The most practical healing spells inflict half the damage healed as subdual damage on the caster, and take a full round to cast. Meaning healing isnt a combat staple, and more of an after combat thing. This leads to setting up different types of combats, and removes people from feeling forced into a "heal bot" mode during conflicts. Our group has a magister and a greenbond/ranger, and both feel they get to enjoy combats more than babysitting the fighter.
Almost all spells have a heightened or diminished version that is one level over and under. meaning every spell you memorize is really 3 options to cast. Diminished versions are often limited to yourself, short durations, etc. Say you just need to levitate for a round or two... you can cast the diminished version (1st level) instead of blowing a 2nd level slot to cast the full duration levitate. 
Additionally, with the proper feats or magic items you can use material components (of roughly 5-20gp value) to add a template to a spell's effect. You might toss a 20gp pinch of ruby dust add the fire template to an attack spell, which inflicts d6 extra fire damage (or 2d6 if the spell was already a fire spell). You might pour a tiny vial of acid on the ground while casting a spell to apply the acid template, casing it to destroy twice as much nonliving matter as normal, or potentially stunning a creature if they take more than 20 points of damage. I liked this feature a lot. 
In short, it seems that magic is a better understood tool, and a factor of people's life
However, there are some things I dislike about the magic system.
Exotic spells: I despise that these spells take a feat to learn as written. It ruins the feel of rewarding a player with a cool new spell by forcing him to blow a feat to use it. This wouldnt be so bad if the spells were more powerful than spells of a given level, but they arent. Its blowing a feat for fluff, which I cant stand. All it represents is that its not commonly taught. However, if someone is sitting down and teaching you it (or you uncover a spell formula), its not rare FOR YOU. We hand waved this, and allowed people to spend exp to leanr them, and gold to research them if they dont have access to the formula (50exp for 1st, 150 for 2nd, 300 for 3rd, 700 4th, 950 5th). Also, lots of "working class mage" spells seem to fall into this category... which is at odds with magic as a tool for society rather than just good for blowing things up. 
Unique spell: You can only have one, and it has to be taken as a 1st level only feat. Its boring to remove the ability for caster players to research new and fun spells, and adds nothing in return. I nixed this as well.
Some of the spells were obviously designed by people with no d20 experience, the 1st level spells in particular. Shock, for example, is a 1st level touch spell that inflicts d4+1 damage and 1 point of dex damage, and allows a save to negate. Another spell is a ranged rouch attack that inflicts d6 subdual and allows a will to negate. Given that there are servicable spells in this range, I dont see why these exist. I buffed up a few of the low level spells both me and my players saw as very weak. 
So, I love the system itself, just some spell specifics irritate me. 
Other classes
Akashics - really cool class, really flexible. I moved their benefits up a level, so they dont have to wait so long to be able to customize themselves a bit more. 
Mage Blade - I changed their stat requirement to Intelligence, since they seemed more thematically linked to a magister. Otherwise its a very good martial/caster hybrid base class, and a niche that was sorely missing in D&D
Rune Thanes - I dont get the point of this class at all. Its noticably inferior to a magister at basically all levels, has a spellcasting on par with an adept, in exchange for being able to set up minor rune traps. I ditched it as no one was interested in playing one, and I saw no need to do a bunch of work rebalancing it.
Witches - what I thought sorcerers should have been - guys with thematically related innate magic powers. I let them cast in light armor though.
Warmains - I dont like this class at all, its a fighter with d12 hd, a slightly better will save, and fewer feats/customization. With the feats you miss out on, a fighter could take improved toughness and iron will, and come out ahead. So, I guess if you are complaining about fighters being overpowered (laugh) this class will work for you.
If you pick up the book, I recommend using the magic system, and letting the bard, rogue, fighter, barbarian and ranger in from the PHB. The non caster classes (aside from unfettered and the akashic) just dont do it for me. The totem warrior is perfectly fine, but doesnt seem to be generic enough for my tastes as a kind of "outdoorsy skilled warrior type guy". Their new class, the ritual warrior falls a little flat too, since it has a 3/4 BAB and gets to use combat rituals (VERY minor self buffs), none of which impressed me much. You can kind of make yourself almost on par with a fighter for a few rounds, after which you're an aristocrat (npc class) with no skills. 
The biggest reason to buy the book is for the magic system and the akashic class. The setting itself didnt do much for me (as generic as greyhawk), so much of my focus is on the crunch.