I've always loved wizard, secondary cleric. Can't help it. I love all the spell slots and tend to avoid casters with less. I really didn't enjoy the psychic personally.
So I'm very surprised and pleased that I like this class as much as I do
Int based prepared occult caster? You have my interest. I prefer prepared casting. Dirge is a interesting flavor. I like you think of it as throat singing.
Create thrall: at a base level you can look at this as a 30ft 1d6 spell attack that can benefit and provide flanking. Just in it's own, that's good. That's amazing. I love that.
Consume thrall: built in focus point regeneration is welcome.
Subclasses: for me it's all about the flesh magician. I don't want to be as close to the enemy as bone spear wants with bone shaper and spirit monger isn't bad but doesn't wow me. Flesh magician giving me something that doesn't immediately kill a thrall (dead weight) but encourages enemies to spend map or be hindered. Plus their class feature creating difficult terrain is fantastic synergy.
Mastery of life and death: seems niche? Like, makes void warp better.
Undead lore: is really cool and combine it with bone speaker and they are instantly a pretty great recall knowledge character with one skill.
Inevitable return: is nice to have though I'd like it if it worked with you liked undead so long as they had a corporeal form.
Feats:
Bone spear: decent for a melee necromancer
Deadweight: amazing, synergizes with it's own subclass ability (they kill the thrall on them and are standing in difficult terrain) and since the thrall isn't consumed or dead, if they don't kill the thrall. Well, you can have some fun.
Life tap: it's good, it's jive that they can move and do their thing making it very reliable.
Reach of the dead: I wish this let me cast touch spells through the thread if I'm honest.
Conceal spell: thematic for some necromancers and I think this could let you spook some town guards.
Muscle barrier: this is fantastic, 2 actions to give someone 10 thp and +1 Athletics, scales amazing. Looking to play at level 7 and that's 40 HP.
Necrotic bomb: very nearly fireball. Incredible value.
Reapers weapon familiarity: first big stinker. At bare minimum this needs to give crit spec to these weapons.
Bony barrage: this is pretty good. Decent AOE that you can also buff your allies inside of and have them avoid damage. Seems a nice alternative to the next feat to get rid of excess thralls.
Draining strike: I want to like this, and on paper, it's pretty good. Extra d4 per thrall is nice. But I'll be honest, the healing is meh. The damage is low. I'd rather it do more damage and maybe apply a condition on hit/crit. You can get a decent amount of healing and temp HP already from other sources.
Bone burst: I love this a lot. If you place multiple thralls on the battlefield then you have a good chance at this pseudo reactive strike.
Reclaim power: I like how this technically scales with your level because you can easily summon more thralls.
Zombie horde: sounds fun but by my reading it's also very cumbersome. It said it deals damage to creatures in it but you can choose to sacrifice a thrall? It doesn't automatically hit the thrall?
Conglomerate of limbs: 40 HP and never gets crit means it might survive a moment. No limit on the number of creatures it tries to grab. Sustain to move. Huge sized (more flesh magician synergy)
Osteo armaments: I want to love this! On one hand, incredible versatility if you can get martial weapon proficiency. On the other hand, it's weak. Or rather becomes weak. I'd prefer the ability to sacrifice other thralls and giving it more property runes as a result. If only for that round. Something like (if you would sacrifice a thrall, gain unholy rune until the beginning of your next turn) or something.
Desperate surge: this is interesting because it means you can be a Dex gish or even just a dedicated caster and do a strong athletic maneuver. This is really fun.
Life sense: this is funny but I'm uncertain you it's value.
Quickened casting: standard stuff
Become as spirit: this is probably my favorite of the three level 12 options, very useful to essentially never be bottlenecked. Get those wands of tailwind ready
Reinforced skeleton: 2 resistances and a lot of speed, honestly what isn't to like.
Vital conduit: double toughness (makes me want to play a dwarf for triple). The sickened effect forces my favorite subclass down a melee path that I don't personally want to go down, so a little sad.
Necrotic focus: it's use is dependant on GM and campaign I think.
Recurring thrall: frankly, incredible. Occupies space, frightened, and it keeps coming back!
Skeletal lancers: creating 5 thralls is reason enough for this? Wait, at this level aren't we already summoning 3 for one action? Maybe up the piercing to 10?
Desperate revival is funny because you could potentially kill a teammate.
Effortless concentration: really nice depending on the thralls you summon
Flesh tsunami: please be 60ft not 30ft. But for two thralls that's some devastating movement denial.
Bind heroic spirit: I imagine this to be the prime gish option, would be nice if it scaled, starting at +1 allowing you to pick it earlier.
Ectoplasmic aura: is this just a constant effect? Because that's pretty strong.
Living graveyard: this enables some great multi thrall use options as you litter the field in thralls.
Mortem ultimatum: what's not to like
Perfected thrall: this seems good? I wonder how quickly it dies though. Can you make the perfected thrall latch onto an enemy with dead weight? Lol
Overall impression: I love this class, if you indulged upon this read you will see I like most of it's features. It's a great resilient battlefield controller/damage dealer/ok gish.
My personal pain points are mainly in reapers weapon familiarity and osteo armaments.