It wasn't so much the extra buffs but the consume damage buff. Jungle Nunu's power is his ability to counter-jungle, which the S3 jungle royally screwed over by making the big monsters stronger (right after his S2 buffs too). Now that he can just walk up and consume things again he's become better at his job, though 600 true damage at rank one is a little much (and is getting nerfed next patch). There is a reason junglers call him Satan.