Necropolis discussions.

Vampires are simply not as durable. I remember in Heroes of Might and Magic IV, 5 vampires were a force to be reckoned with. But in this game, even 20 of them don't seem to do much.
However, when their numbers exceed 90, they become a real threat – they overwhelm with sheer numbers, swarming and taking down mages and titans alike...
They have a significant advantage – they are effective at blocking smaller ranged units (elves, crossbowmen, etc.).
Liches are powerful, and dragons seemed stronger to me.