Of all the bosses in Dragon Soul, I didn't expect heroic Ultraxion to be so much fun compared to normal mode.
I've always viewed Ultra to be a rather boring fight - DS's Patchwerk; the obligatory tank n' spank.
However, making Fading Light a variable time - plus the added bonus of having to stay out for Hour of Twilight every now and then - somehow makes the fight a lot more interesting.
No, I don't know why either - possibly the extra adrenaline from almost missing Fading Light occasionally when it's on a short timer? Who knows! In any case, I'm a fan and can only hope that the other heroic fights improve on the normal modes as much as this one :)