I like the gross sludge. There needs to be a strong current of disturbance and unease, I need to be disoriented. Primal and fucking menacing and fucking gross. Like a rapist leper, or a beautiful girl eating feces. The music, and the lyrics, need to speak of these things.
Neurosis is classic but I think Lord Mantis has taken over as the true spirit of sludge for me, even if they are technically a variant.