they already have a pretty decent defense - looking to get another CB, Rever being mentioned - and a very good midfield with Cana, Ledesma and Hernanes in there (rumours about interest in Arouca from Santos too).
The only thing they really needed was strikers, who know how to materialize all the chances the create, and with Cisse and Klose, I think they got those.
Unless they implode, I expect Lazio to be a very serious contender for the 3rd spot next year