I don't claim to have a monopoly on this discussion, but as he is my fav lock, I looked at him and did a comparison from his MKI rules.
The first change is that his Spray Template is now a SP 10. Awesome
Glory of Everblight just changed name to Manifest Destiny and now affects models in his battlegroup.
Black Chasm changed to Scourge. It went from a 4 inch AOE to a 3 inch and lost a point of POW.
Unnatural Aggression changed to moving during maintenance phase and must move towards the nearest enemy model, as well as triggering on damage of any kind.
The most disappointing thing of the Big Guy is that he has the fewest beast points of the casters.
On a side note, he DID lose Hubris. Not that it was that difficult to deal with, but still nice.