I haven't played it yet, but almost all Covenant are larger or equal to normal Human size. Elite's are the most capable warriors though.
I havent seen a single Elite on my play time so far. Only Brutes on different classes types. (Armored-Shielded-Shielded and Armored) The classical easy kill grunts (I got the Headshot pistol achievement with them) And the Jackals with Carbines and Snipers.
But those plasma shots where i found Buck dead were strange :o
Also the Plasma Rifle is now red :D Maybe because its the Brute Rifle
Finally, the Brute AI is now actually pretty equal to an Elite AI, you know, tumbling when a grenade is thrown or running at you when you stick them a plasma grenade.
Also, i found pretty hard to stick someone a grenade, i have only been able to do it while sneaking.