Controllers/Summoners have never really been that impressive to me, just by fact that when you animate something as a skeleton/zombie, it looses pretty much everything that makes it awesome in the first place. Class levels, special attacks, etc. The more powerful undead are much better but are also much harder to control (Good will save and high charisma makes losing control of your ghost/vampire/devourer a very real possibility).Unfortunately, divine casters make the best summoners/controllers but they also lack the most important spell for when you do inevitably lose control of your power-house (Control Undead is high level and Sor/Wiz only!) :(
That said, SoS/SoD Necros are incredibly powerful. You dabble in undead but ultimately they're just a distraction to keep the enemy busy while you unleash SoD after SoD at them. Wizards are the best here, and only better than Sorcerers due to the School Specialization being quite superior to the Undead Bloodline.
Just my 2cp.
Its true, skeletons and zombies pack less of a punch than what they originally were, but I wouldn't say they lose everything. (Consider the T-rex, whose powerful bite is a special QUALITY, and as such, is not lost when skeletonized.) As for higher-level undead, I go by the philosophy that said undead could choose to join you willingly, being intelligent, and that you could argue that either way, they will serve you, its up to them if they want to maintain control of their faculties.Also, who says that the Undead bloodline is weak? Consider their bloodline arcana, which means that a solid percentage of undead can fall under your sway with a mere charm person and the like, thus meaning you don't have to take command undead or control undead until later, or not at all, given that most undead used to be humanoids, and depending on how many undead the GM throws at you.
Necromancers are pretty OP until you realize they are countered hard by any good aligned cleric or paladin, not to mention all the other class features and archetypes that can make you feel generally worthless, but the big issue I have with necromancy is theres literally no reason not to have a pool of animated undead if you're playing as a wizard or evil cleric, but from my experience people only use the spell if they are theming their character around necromancy. Every neutral wizard should have a pool of animated dead in a portable hole somewhere. They can be a total game wrecker, especially when fully buffed. Another saving grace for it being so OP is that it's generally illegal in most campaign settings.
Well, when in Rome...
The biggest advantage of a Necromancer is you can cast the Animate Dead spell during downtime. You get the benefit of basically a permanent 4th level spell until the undead you create are destroyed. While skeletons and zombies aren't particularly strong monsters they do make for decent meat shields.
If you are in the middle of a political campaign where you are fighting against a bunch of leveled humanoid types...the undead you'll be able to make are pathetic. On the other hand if you're adventuring through the Age of Dinosaurs generally speaking they are more powerful when made into zombies. A while back we did the Kingmaker AP, and I can think of a few notable creatures we took on that would of made for frighteningly powerful zombie.
If you are going to run a necromancer, never waste a potential zombie. Make sure you bury them and you have a map marked where to find the bodies when you want to use them later. There are more than enough spells that will let you recondition the body to a state you can use them as long as they aren't incinerated to ashes.