Kevin Campbell in terms of immediate impact, we looked as though we were pretty much down before he joined.
Tim Cahill and Arteta had more of a prolonged impact, they added a lot of quality and guile to a very mediocre midfield.
Lukaku in terms of adding an instant goal threat, that first season under Martinez he was ridiculous and helped the players behind him play better due to the space he created.
We need another instant improvement player as soon as, otherwise we will stay where we are for a long time.