Larfleeze has been somewhat nerfed in terms of his power levels in recent times but, when he first appeared in 2007, his power made Superman's seem almost irrelevant.
He arrived during the build-up to the Blackest Night storyline, as the sole representative of the Orange Lantern Corps - the Corps powered by the emotion of avarice or greed - and was essentially a one-man Corps. He was powerful enough to take on entire other Corps on his own and was powerful enough to take on the cosmic Guardians by himself.
His huge power was derived from his close proximity to his Corps' power battery - an item that normally empowers hundreds, if not thousands, of individual Lanterns. As a result, he could actually use his own mind to maintain a Corps' worth of construct - essentially giving him a back-up army under his own power.
Like any other Lantern, Larfleeze also possessed enhanced physical statistics and immense energy-based powers, but it is the fact he has the power of a whole battery to himself that ensures he has cosmic power beyond that of Superman's by some distance.