I'm generally happy with the book. Granted, I won't use 75% of it's contents, but what I will use is worth it. My favs:
Spells:
-Unluck (4th Wiz): that is now a must have spell for my arcanists. For one round per level the critter must basically reroll all his dice and take the worst result. Granted, spell res and will save apply, but if they're missed, it will be such a joy to see the DM go "CRITICAL ! Oh wait... no... never mind...". The fact that it's a Divination spell, NOT a mind affecting or somesuch, means that most critters with a will save score will be affected.
-Orb of Fire (4th Wiz): also sweet spell. No save, no spell res, max 15d6. And if a fort save is missed, dazed for one round. Sweet.
-Resist Energy, Mass (4th Wiz, 3rd Cleric): This is an awesome spell. Blue Dragon attacking ? After the cleric's init, EVERYONE laughs at his breath weapon.
My friend complained that the 4th level arcane spells weren't much. I told him that from now on, the sorceror will be hard pressed in choosing his 4th level spell.
Feats:
A lot of repeats from previously published stuff, but it's nice to see them all nice and lined up in a 3.5 book.
-The Draconic feats are quite cool for sorcerors. I'm already considering taking Draconic Heritage and Draconic Flight. Basically it means that in my first round, I can cast a spell AND take off to get out of reach of melee critters. For me, in the game I currently play, the first round was always tough, often casting Improved Invisibility for defense followed by an offensive spell in the next round. That quite often weakened our offensive, and the players sometimes convinced me to forego my defense to attack right away... my sorc bought the farm in the last game.
-Return of Persistent Spell. The cost is now a slot 6 levels higher, so it means that if your cleric wants shield of faith AND divine favor up at all times, well he's going to burn two 7th level spell slots. I think that's a price quite high enough.
-A bunch of Sudden feats (Sudden Empower, Sudden Maximize...). Basically it lets you automatically apply the feat to the spell at no extra cost, but only once per day. Worth it ? I think not. Sudden Quicken has 6 feat prerequesites, so I don't think we will see it picked that much.
-Arcane Preparation. Lets spontaneous casters prepare in advance metamagicked spells with no restrictions. Very nice. It's not clear if this allows the sorceror to pick up Quicken though...
Prestige Classes:
Meh. I'm not a super fan of prestige classes, so it's very hard to please me. At first glance there doesn't seem to be any Frenzied Berserkers or Servants of Pelor, so it's a good start. The two PrC's that made me go "Heh... cool!" are:
-Wild Mage (10 level PrC): I have not seen the previous 3rd or 3.5 edition versions, but this one looked very fun.
-Fatespinner (5 level PrC): That is one cool PrC. Over 5 levels you only loose one level of your basic arcane casting, so the cost is minor. What it does gain, however, is giggle inducing. He gains really just 4 powers, and each of them usable only once per day, but very rougly you can reroll one of your dice, make a FRIEND or FOE reroll one of their dice, give a FRIEND or FOE a +10 or -10 on their next saving throw, and add up to +5 to any die roll you make before making it. All these at the cost of one casting level, count me in !
New Classes:
(*) I must say, I don't think the warlock will see much use IMC. It's nice to cast these spells at will, but a 20th level warlock only has 4 evocations. Four. He definitely got the shaft on that one. And his eldritch bolt maxes at 9d6 at 20th level, which is negated by spell resistance. A 16th level sorceror can easilly inflict 30d6 (Orb of Fire, Twined), NO spell resistance. The critters at those levels will laugh at my measly 9d6. Thanks but no thanks.
The Warmage OTOH easilly replaces the sorceror as arcane artillery. Very strong in that field. ALL his spells are offensive, but he knows ALL of them as soon as he reaches a new spell level, and can spontaneously cast any of them. Think of any offensive spell in the player handbook (AND complete arcane), there's a good 90% chance that he has it. Better hit die, nice supplemental abilities nicely spread out throughout the 20 levels. The drawback: those spells that a sorceror often learns (identify, false life, slow, dispel magic, invisibility...), he can't cast them, so if your party depends on you for the basic arcane spells, they'll be giving you funny looks. And I don't mean funny ah ah.
So, that's with my first quick read of the book. I might be mistaken about the warlock after I study it more, but I'm not holding my breath.
(*) Edit: I was wrong about the Warlock. at 20th level, he knows 12 invocations, and thus kicks major arse. Sorry for the wrong analysis. And at second glance, he does more than 9d6 with his blasts, he can actually add other effects to just the 9d6.