A good description is that they are amplifiers. They magnify everything in your sensorium to the point of distortion. Every thought, sound, emotion; all are pumped up to eleven. You don't have separate senses; they all blend into interacting feedback loops of synesthesia. Your thoughts become tangible, perceivable objects and sensations. It can get overwhelming and almost requires a light-hearted attitude.
It can be enlightening, fun as hell, or deeply terrifying, all depending on your attitude as you go into it.