It needs someone with a pirate accent, for certain.  Why?  Simply because pirates are vaguely a part of Halo (emblems).  Being blind in one eye, i feel an urge to defend our depth perception-challenged friends.

But seriously, it needs a wider variety of accents, i'm getting bored with the same two or three accents you do hear. And to counter what i've read so far:  There is no such thing as no accent.  What you percieve as no accent is simply the accent you are accustomed to, and thus, do not notice.  And being monotone is technically an accent, so that doesn't count either. 

(Incase you can't tell, the first part of my post was a joke)