Glade Riven
Adventurer
Made for 4e, but still applies:

While I own the game, I haven't had the opportunity to play it (just managed a few yoinks), so I'm fuzzy on the details.
To what are you referring?
If you're just talking about the lack of favored classes, I can see either side of that mechanic.
[...]
Magic
I saved this for last, because this was the single most significant change from 3rd edition, and the best.
First of all, all spells were combined into a single master list, that are subdivided into three classifications of Simple, Complex, and Exotic spells (Still keeping 0-9th level though).
All spellcasting classes get a certain availability of spells, first in levels, then in simple to exotic.
For example, the Magister gets access up to level 9 spells, and learns all simple and complex spells. Greenbonds also learn up to level 9 spells, but only learn simple spells... and spells of any type that possess the Plant or Positive Energy descriptors.
Meanwhile Mageblades get up to level 7 spells, of simple only.
Second, each class specifies what kinds of components they use. If they use somatic components, they worry about armor spell failure. For example, the Greenbond uses verbal only; the mageblade uses verbal and somatic, although he can ignore spell failure while using his athame; the magister uses verbal and somatic, and is penalized without his staff; and the witch uses verbal, somatic, and material, although they can make a spell effectively psionic by quadrupling the spellcasting time and ignoring all components needed.
Thirdly, almost all spells in their descriptions have a diminished and heightened version; a diminished version is weaker but burns a spell slot one level lower, while the heightened one is more powerful but burns a slot one level higher.
Fourthly, and this is the very cool part: spellcasters, all of them, prepare spells somewhat like wizards, but cast spells like sorcerers!
Let me explain. A spellcaster may take an hour (and not just once a day, but any time) to prepare a number of spells as dictated for their class. Due to how spellcasting works, they never prepare more than one copy of a spell.
A second chart shows how many spells they can cast per day. Each time, they burn a spell slot and select the spell they will cast. The prepared spell doesnt disappear, just the slot. So, you could cast one spell multiple times or a different spell each.
In other words, you are like a sorcerer that can change his spells from day to day - or even hour to hour.
Also, there are a wide variety of feats that let you play around with the spells, usually at a cost. For example, the Psion feat says you get enhanced access to spells with the psionic descriptors: this means a greenbond would gain access to complex psionic spells instead of just simple psionic spells.
Then, it lets you apply the Psionic template to any spell; the psionic template lets you cast the spell with no components, just conentrating and firing off. This ladens the spell unless the spell already had the psionic descriptor. Ladened spells burn two slots of their level instead of 1.
Finally, spellcasters can do whats called Spellweaving: a spellcater can weave three slots of a lower level to gain a higher slot of the next higher level, or break up a slot of one level to gain two slots of the next lower.
Between all of these, the flexibility of the spellcasters are nothing short of phenominal!
This flexibility comes at a cost, however. In general, the spells are weaker. There are no instant-death spells (although a few come real close), healing spells are weaker, etc.
For instance... there is no magic missile. the attack spells of first level exist, but are weaker without a doubt. This allows you to keep these guys balanced with Core classes should you ever mix the two.
Also, the idea of true names: if you chose to be unbound, certain hostile magics cannot attack you. For instance, most curses require your knowing someone's true name (which is hard, but not impossible, to learn); if they are unbound, this is obviously impossible. However, most curses are also INCREDIBLY long duration, many in essence never going away unless a remove curse is cast - which also requires a true name.
By the same token, however, if you are unbound, you don't get access to the better Ceremonial feats, and you cannot be targetted by certain beneficial spells... such as any spell that would raise you from the dead.
Finally, spellcasters can do whats called Spellweaving: a spellcater can weave three slots of a lower level to gain a higher slot of the next higher level, or break up a slot of one level to gain two slots of the next lower.
What is your opinion on spellcaster multiclassing under this system?
PS. I have already experienced the changes introduced in AE/AU, however I'd like to know how your RAW-based stance is affected by this alternative.