I have a bit of sympathy for Dark Magus's point of view here. Though I have been mulling over a necromancer character to play in a friend's upcoming megacampaign, so I may well be a little biased...
Any specialist has to sacrifice two schools to specialise. The choices (and associated handicaps) are:
Abjuration. Lose abjuration and you lose dispel magic. Big no-no. Even if you can cope with that (how?), you lose almost every single spell that can protect you from area-effects - energy resistances, globes of invulnerability, save boosts - the lot. First couple of low level evokers you face, you're going to be fried.
Illusion. A possibility. Losing invisibility hurts, and the image spells are great utilities, but Illusion can be sacrificed. you lose a lot of your potential for subtlety this way, though.
Evocation. Losing pretty much all the area-affect blasting spells hurts (shadow evocations notwithstanding) since there is pretty much no other spell in the Wiz spell list that requires Ref saves, but sending is also a deceptively big loss (why is Telepathic Bond, which establishes a lasting mental communication, a divination while Sending, which establishes a brief mental communication, an evocation? Especially considering Demand is an enchantment!). Sacrificing evocation is almost an option for a cunning wizard but the lack of low-level attack spells is a real problem.
Conjuration: very hard to justify sacrificing, given its flexibility. From Mage Armour at low levels, to the summoning and calling spells at higher levels, to teleportation, plane shifts and gates, a wizard giving up conjuration is sacrificing many of the classes most powerful and iconic abilities.
Enchantment - other than Illusion, this is the subtle school. Optional for a battlemage (though there are some real killers in there), but in a non-dungeon campaign with politics involved, enchantment is vital. Charm is an almost indispensible interogation aid, as well.
Transmutation: A bit like conjuration, there are a few absolutely essential everyday wizard abilities in here. Flight, levitation, lock-opening, stat boosts. Water breathing and polymorph may sound minor, but when you need them you really need them. Transmutation has Passwall, Gaseous Form, Knock, Stone Shape, Ethereal Jaunt and Polymorph. Without these, how does a wizard even get into a locked, unguarded room without blowing the place apart? Forsake Transmutation and the rest of the party will be readvertising your position after the first adventure.
And then there's Necromancy. There's some great spells in here (Enervation, False life, Circle of Death, Horrid Wilting), but not that many which do unique, vital jobs. Finger of Death? Disintegrate can do the job. Magic Jar? Dominate can fake it. Wave of Exhaustion? If that's your best 7th-level battlespell then you're probably in trouble. You can give up necromancy and not miss out on much, unless you're the build-an-army-of-undead-to-conquer-the-world type (and even then Conjuring and binding fiendish creatures might be a better bet anyway)
Necromancy is quite strong in certain areas. Creating undead isn't really an option if you're trying to run a good or neutral game, but there are others. There are a fair few damaging spells (some disallowing saves) but a depressing amount (vampiric touch, contagion, chill tough) require a touch attack - not a good move for a wizard. Things like Clone, Magic Jar and so on are very handy in the right situation, but not exactly everyday necessities. I was thrilled when I read the 3.5e spell list and saw Eyebite as a necromancy, but since it is no longer a gaze attack and no longer gives charm or sleep options it was somewhat of a letdown. Symbols can be ok, but the 10-minute casting time is a big drawback. Even Circle of Death, one of the truly powerful necromantic attack spells, suffers from a prohibitively expensive material component compared to, say, Chain Lightning. There is also a considerable variance in utility over the spell levels - it's hard for a 15th-level necromancer to find something useful to put in his bonus 1st-level spell slot, while an extra Magic Missile, True Strike, Charm Person or whatever is always handy. To top it off, a lot of spells that could otherwise be useful (Eyebite, Symbol of Death) got lumbered with the Evil descriptor. It's almost as if the rules are actively trying to discourage people playing 'white' or 'grey' necromancers. I would have preferred 3.5e necromancy to shuffle fear effects off to Enchantment where they belong, and to include a lot more spells that affect the living body or its processes (like Haste, Slow, Bull's Strength), just to add a bit more flexibility to the school, but that's a topic for a whole other thread.
A less-obvious hit to necromancy under the 3.5e rules was the changes to Spell Focus. Necromancies, especially the higher-level ones, are typically either Moderately Unpleasant Effect, No Save, or Cataclysmic Effect, Fort Save For Bugger All. The ability to significantly boost DCs on the latter grouping was one of the big weapons in a necromancer's armoury.
My necromancer character was intending to forsake Evocation under 3e rules (and since that was a greater than necessary sacrifie, I was hoping to bargain for a bonus feat out of the deal as well) But this is no longer an option. I have to choose another school as well. As stated above, I regard Abjuration, Transmutation and Conjuration as essentials if you're not going to completely hamstring your character. The character concept is of a subtle, politically minded type, so Illusion and Enchantment are necessities (as is Divination, which is beyond the scope of this discussion anyway). So what do I do? The answer, apparently, is swear under my breath, show this post to my GM, and hope that he sees things the same way I do and cuts necromancers some slack.
I mean come on. Evil Necromancers are supposed to terrorise fantasy worlds. How can they do this if they can't summon demons, or teleport, or make their minions look like fair damsels, or put the king under their spell, or level city walls to let their rotting legions in, or even erect spell defences worth a damn. If any of these evil wizards chose necromancy because of the forbidden power it offered, they would probably have been better off getting a good nights sleep, drinking a nice mug of hot chocolate, and having another look at Conjuration instead...