Well, he's made two European Cup Finals, winning one of them, and took them to within 2 points of winning the Prem last season (losing just 2 games all season, whilst doing the double over Man U and Chelsea). That ain't bad.
I'd say that a huge amount of that was down to the determination and incredible skill of Gerrard - yes, one man can make that much of a difference (as was proved last night for example and when they won the Chamions League final).