Signing Mesut Ozil was a major step forward for Arsenal, but the signing that could prove more pivotal for the club is that of Emiliano Viviano.
You couldn't possibly argue that bringing in Ozil didn't help Arsenal. He's a world-class midfielder and an assist machine. Olivier Giroud and Theo Walcott will improve as they receive tremendous service from the German midfielder, and Santi Cazorla is helped out as he no longer has to carry so much of the creative burden in the final third.
In terms of whether or not Ozil would make Arsenal title contenders, that's a little bit more up in the air. The Gunners weren't in dire need of a creative midfielder at the top of the attack. Obviously, since Ozil was out there, Arsenal couldn't possibly have passed up the opportunity.
It's not as if signing him was a mistake. It just didn't go far enough to cover up Arsenal's other major issues; hence, it's actually not the best signing of the summer.
With Viviano, Arsene Wenger was able to solve what has been one of the growing problems of the last few seasons: the stagnation of Wojciech Szczesny. The 23-year-old is still a supremely talented goalkeeper. However, his performance level has slowly been dropping. It's a bit the same as what you're seeing with Joe Hart and Pepe Reina.
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Szczesny still has plenty of time to get his career back on track. There would have been no sense in trying to find an outright replacement for the player. He hasn't been so bad that you think he's a lost cause.
One of the biggest reasons for Szczesny's mini-decline is that he hasn't had a presence like Viviano pushing him. In the past, if he had a bad performance, there wasn't anything Arsenal could do about it. He could continue just flapping at crosses and making poor decisions, and he wouldn't have to learn from them in order to keep his place in the first team.
Manuel Almunia, Lukasz Fabianski and Vito Mannone aren't the kind of players who could truly make a claim to be a first-choice keeper on a Champions League squad, so Szczesny was one of the first names on the team sheet, for better or worse.
In addition, there wasn't really anything he could learn from that trio of players. They couldn't really give him pointers as to how best to improve.
What Szczesny and Arsenal both needed was a more stabilizing presence between the sticks.
Viviano is that kind of player. He's an experienced goalkeeper who's featured for the likes of Fiorentina, Palermo and Bologna. His positioning and pitch IQ are very good, and he knows how to handle crosses into the box. Having played in Serie A, the Italian will be no stranger to a more physical style, either.
Wenger will have enough faith in Viviano to put him in during crucial league or European matches, if push comes to shove.
In addition, at 27 years old, there's no real threat of Viviano being the long-term option.
When Viviano's loan is up or in a few seasons should the deal become permanent, Szczesny will be the unquestioned top keeper and should take his throne as one of the best in the Premier League.