It plays to the board and doesn't boast a lot of instant-speed trickery, though it has quite a few branching subthemes that it supports quite well
Players may like it more for its novelty than sheer value
(Each in the mana costs of permanents you control counts toward your devotion to black.) Your opponents can't gain life
Ghired, Conclave Exile is really good at this - once you've got a massive token like a Desolation Twin, you can populate every time you attack, hitting for more and more every combat
Multiple instances of haste on the same creature do not stack, So, if you give a creature haste twice, it doesnt get any extra abilities
Its another kill on sight creature, though, so be ready to keep it safe with countermagic or similar