It's not like there's some massive diffence in gameplay when playing as the arbiter as opposed to the Chief. Important thing is that the arbiter is involved in the story.
And he's playable in co-op, so you can actually play through the whole game as him.
I'm a huge fan of both the character and his levels in Halo 2. Using the recharging camo was one of my favorite additions to Halo 2. So yeah, I'm kind of bummed. But on the flip side, there's something kind of appropriate about finishing up the trilogy as the Chief. I'm sure I'll recover if the campaign is what I hope it is.