Running D&D: Engineering Player Buy-In, Part One

Ah, Dungeons & Dragons . . . what can I say that hasn't already been said? What's the best thing about it? Is it playing a character? Running a campaign? Roleplaying a quirky gnome illusionist? Creating an epic 20-level dungeon filled with ghastly horrors and deadly traps?

Well....that's no easy decision.

How does one gauge his response?