I was originally drawn to the Tau because they were the exact opposite of my Space Wolves. On top of that, having never been a big fan (and hence, never really watched it) of anime, I liked the smooth, clean, elegeant and practical lines combined into single forms. They are simple and efficient. The sheer amount of capability packed into the crisis suits is astounding, especially when compared to other units of comparable cost and loadout. The vehicles are designed with survivability in mind, and the destructive potential of the rail and ion cannon is unparalleled.
The backstory is awesome, and the concept of a government so completely supported by its population and working so well is incredibly appealing, considering how foreign the actual concept is. The actions are so much easier to visualize when reading fan fiction, especially when you've seen the models painted by the people who are writing. *coughWhiteKnightcough*
The fire warriors are simple and easily painted, and with a minimum of "decoration." It really reminds me of today's uniforms, with just enough markings to denote unit, rank, and position, and at the same time effective in the field (when painted that way, anyway
Anyway, that's what drew me.