I also forgot to metion Big Eyes Small Mouth d20 from Guardians of Order Even if you aren't into anime roleplaying it is still worth a look for how they manage to make a point based (advantages and disadvantages) character creation system work with the d20 rules. If you are one of those people who feel that classes and levels are too restrictive then this book is worth a look.
As to the question "how are the AU rules different from stock DnD?" Well many of them aren't, espically a lot of the combat rules. AU introduces a few new ideas including "traits" which are feats that can only be taken at first level and "ceremonial feats" which are slightly more powerful than regular feats but have some more restrictive requirements and also the idea of True Names: a character who has a true name has access to certain powrfull feats (usually ceremonial feats) and abilities and can benefit from some special spells but is also vulneurable to magical attack from enemies who know his truename, characters without a truename don't share those advantages or disadvantages but gain a bonus feat at first level instead. AU also introduces "racial levels"; races other than humans can take levels in a "racial class" which is sort of like a prestige class except the only requirement is that you be of that race and as you gain levels you gain abilities that make you more a paragon of your species, for example the giant racial class eventually makes you size large, most racial classes are only about 3 levels in total. And don't undersell the variant classes either, many of them are among the best designed I've seen in a long time. I espically like how flexible they are, many include notes by Monte himself about how to tweak the class for different flavors. For example, the Champion class is a warrior with a cause, the book includes rules on how to make a champion of light or justice or darkness and severall others as well but also suggestions for making a champion of any given cause (such as champion of a particular kingdom).
But the real attraction, for me at least, is the magic system. Spellcasters still use a number of spell-slots per day but they do not memorize spells. Instead they have their spell slots per day like a sorcerer and then they have another table of spells they can have known per day, this is similar to a sorcerer's spells known table in that he fills it with spells he knows and he can spontaneously cast those spells using his daily slots. However, like a wizard, he can change which spells are in his spells known each day (and he doesnt' even need a spellbook to do it either). This gives spellcasters an enermous ammount of flexibility and prevents them from becomming booring casters who always use the same spells over and over. Fruthermore the spell-list is broken up into simple, complex and exotic spells. Think of this like simple, martial and exotic weapon proficiencies. Most spellcasters only know simple spells and have to buy the rest with feats, the dedicated spellcasters (such as the magister) know simple and complex spells. The spells themselves are also more finely balanced than stock DnD. In DnD spells tend to increas in power exponentially with level (3rd level: fireball, 9th level: meteor swarm) but in AU the curve is much closer to a linear curve. This helps offset some of the power casters gain from flexibility and keeps magic from dominating the game at high levels. Also direct effect magic and "blast magic" has been toned down in general; a spell the equivalent of Mage Armor is an exotic spell and there is no spell equivalent to Magic Misile (that's on purpose). But there is more as well! You can also "weave" spell slots: break a spell slot up into multiple lower level slots or combine lower level slots into one higher level slot. You can "laden" a spell, use two slots of the appropriate level to cast it, which will often give you extra benefits. Lastly each spell has a diminished and heightened version: a diminished spell uses a slot one lower and has reduced effects, highten a spell by using a slot one higher and get an extra effect, all with knowing the same spell. Oh and there is no difference between arcane and divine magic either, every spellcaster can potentially case healing spells and blast spells (though some classes are better at one than the other). Like I said, if you are looking for a magic system for a high-fantasy high-magic game there is none better than AU.
Hope that helps.
As to the question "how are the AU rules different from stock DnD?" Well many of them aren't, espically a lot of the combat rules. AU introduces a few new ideas including "traits" which are feats that can only be taken at first level and "ceremonial feats" which are slightly more powerful than regular feats but have some more restrictive requirements and also the idea of True Names: a character who has a true name has access to certain powrfull feats (usually ceremonial feats) and abilities and can benefit from some special spells but is also vulneurable to magical attack from enemies who know his truename, characters without a truename don't share those advantages or disadvantages but gain a bonus feat at first level instead. AU also introduces "racial levels"; races other than humans can take levels in a "racial class" which is sort of like a prestige class except the only requirement is that you be of that race and as you gain levels you gain abilities that make you more a paragon of your species, for example the giant racial class eventually makes you size large, most racial classes are only about 3 levels in total. And don't undersell the variant classes either, many of them are among the best designed I've seen in a long time. I espically like how flexible they are, many include notes by Monte himself about how to tweak the class for different flavors. For example, the Champion class is a warrior with a cause, the book includes rules on how to make a champion of light or justice or darkness and severall others as well but also suggestions for making a champion of any given cause (such as champion of a particular kingdom).
But the real attraction, for me at least, is the magic system. Spellcasters still use a number of spell-slots per day but they do not memorize spells. Instead they have their spell slots per day like a sorcerer and then they have another table of spells they can have known per day, this is similar to a sorcerer's spells known table in that he fills it with spells he knows and he can spontaneously cast those spells using his daily slots. However, like a wizard, he can change which spells are in his spells known each day (and he doesnt' even need a spellbook to do it either). This gives spellcasters an enermous ammount of flexibility and prevents them from becomming booring casters who always use the same spells over and over. Fruthermore the spell-list is broken up into simple, complex and exotic spells. Think of this like simple, martial and exotic weapon proficiencies. Most spellcasters only know simple spells and have to buy the rest with feats, the dedicated spellcasters (such as the magister) know simple and complex spells. The spells themselves are also more finely balanced than stock DnD. In DnD spells tend to increas in power exponentially with level (3rd level: fireball, 9th level: meteor swarm) but in AU the curve is much closer to a linear curve. This helps offset some of the power casters gain from flexibility and keeps magic from dominating the game at high levels. Also direct effect magic and "blast magic" has been toned down in general; a spell the equivalent of Mage Armor is an exotic spell and there is no spell equivalent to Magic Misile (that's on purpose). But there is more as well! You can also "weave" spell slots: break a spell slot up into multiple lower level slots or combine lower level slots into one higher level slot. You can "laden" a spell, use two slots of the appropriate level to cast it, which will often give you extra benefits. Lastly each spell has a diminished and heightened version: a diminished spell uses a slot one lower and has reduced effects, highten a spell by using a slot one higher and get an extra effect, all with knowing the same spell. Oh and there is no difference between arcane and divine magic either, every spellcaster can potentially case healing spells and blast spells (though some classes are better at one than the other). Like I said, if you are looking for a magic system for a high-fantasy high-magic game there is none better than AU.
Hope that helps.
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