It's surprising how few series really dive into the mechanical weight of necromancy as a magical discipline instead of just an aesthetic. The obvious standout is 'The Tide Lords' series by Jennifer Fallon—not strictly necromancy in the classic sense, but the manipulation of life, death, and essence is so systemic it reads like a textbook on metaphysical energy conversion. The rules have real consequences, and power accumulation feels earned, not bestowed.
For a more traditional yet intricate take, 'The Bone Witch' by Rin Chupeco builds its necromancy around a complex system of tea ceremonies, memory threads, and geas-binding. The magic isn't just waving a hand; it's a cultural practice with strict hierarchies and physical costs. It loses a bit of steam in the later books, but the foundational system is brilliantly detailed.
I'd also toss in 'Gideon the Ninth' for its utterly bizarre blend of necromancy, skeletal constructs, and locked-room mystery, though the system is deliberately opaque and more about vibes than clear rules. It rewards rereading to piece together how the thanergy and thalergy actually work. Honestly, most recommendations I see are just 'dark wizard does spooky stuff,' but true complexity requires the magic to feel like a world-built science.