Aesthetic. Being able to use a Greatsword and be a tank is something I've rarely seen in the 1,000+ MMORPGs I've played since 2003.
While the "speed" and "complexity" was neat, it's a "take it or leave it" thing for me. I don't generally look for that kind of stuff in something like a Tank. I just want what I play to look cool, feel cool, (and not be dead last in terms of performance.)
