I'm not very good, but I'm enjoying Poison. She makes me want attempt to properly learn how to play again.
I like how her fireballs work. I get great satisfaction of using the right speed of a fireball to trick the opponent into jumping on it, and trying to create some tricky situations using the slow fireball.
If you catch someone in the air with a fireball you can reset them with a normal like st HP/cr MK/ st HK into stuff like more fireball pressure. Landing that reset is so satisfying.