Ozil is a top world class player, who is bringing the best out of others IMO. Also probably gave the squad a boost knowing that he was joining. They need a CB to replace Mertesacker and probably a decent keeper, and they aren't far off a title challenging side.
Ramsey has been superb, Giroud has looked a real handful, only thing you'd worry about is their strength in depth but saying that they have a few players out at the moment.