Sure, at first, the peacefulness of absolute sensory deprivation would probably feel pretty relaxing.

But then, it never ends. An eternity (or as long as your brain was kept alive) of nothing. You see nothing. You hear nothing. You feel, taste, and smell nothing.

If you're lucky, you'd start building a fake reality to imagine yourself in, like a dream. Over time, maybe you'd accept this reality as being real. People that lose a sense such as sight often gain an enhancement in another sense such as hearing. Maybe with the loss of all senses, the brain's imagination could gain more power.

Maybe it wouldn't be that bad, after all.