There have been some people in the media who have claimed that Arsenal's signing of Mesut Özil does not transform the team, and is a panicky waste of money, given that Arsenal already have Santi Cazorla, Jack Wilshere and Tomas Rosicky. Those people could not be farther from the truth. Despite Özil playing in a position where Arsenal appear to have strength in both quantity and quality, he helps Arsenal solve a major problem from last season: creativity. It's an issue that has continued this season, and was evident on the opening day of the season, when Arsenal didn't create anything of note between going up in the 7th minute and falling behind 2-1. Although they created more chances than Tottenham, Arsenal were restricted in creating chances, both by a lack of possession but also because Arsenal's main creative threat is Santi Cazorla. While Tomas Rosicky is a lovely player, his final ball is not as penetrating as Cazorla's, and by isolating Cazorla, it becomes easier to stop Arsenal. This will all change now. Özil gives Arsenal the type of creative quality they haven't had since Cesc Fabregas left the club, and, at 24, isn't even in his prime.
Özil, though, is different to Fabregas. Fabregas's movement was vertical: he was an excellent goal-scorer, and took up great goal-scoring positions when a striker vacated the central role, which is why he was excellent in 2007/08 and 2009/10, even as Robin van Persie got injured. He was also as likely to come deep, and allow someone like Jack Wilshere or Alex Song to push forward. Özil does drop deep, and because of that, Jack Wilshere may find his forward bursts don't negatively affect the defensive balance of the team. Özil's movement, though, is less vertical than Fabregas, and is more lateral. Because of that, he should swap easily with Santi Cazorla, who will be played nominally on the left, and will also fill gaps on the right when Theo Walcott makes diagonal runs. What this gives Arsenal is a threat from all areas, as Özil can play devastating passes from the right, left and centre, and is no less effective when he moves to a wider area than in the middle.
Özil's arrival is good news not only for the team as a whole, but, in particular, Theo Walcott, Olivier Giroud and Aaron Ramsey. Walcott has become more and more adept at making diagonal runs behind the defence, and was found by Cazorla several times on Sunday. With Özil, Arsenal now have two outstanding talents to play through balls for Walcott's diagonal runs, which should also help Olivier Giroud, who has become very good at making near post runs, to find Walcott's cutbacks--cutbacks that are made often when Walcott's been played through.
Aaron Ramsey should also benefit from Özil's arrival. The Welshman has started the 2013/14 season in fine goal-scoring form, notching three in the two legs against Fenerbahce. He's continued his habit of making excellent off-the-ball runs into goalscoring positions, often providing the third or fourth man on a counter attack. With Özil not as vertical in movement as Ramsey, Ramsey can exploit the space that Özil doesn't take up, and make runs from deep, as he did here when he was found by Jack Wilshere, a move that can definitely be replicated by Ramsey and Özil.
Özil is exceptional at one-touch counter-attacking football, a style of football Arsenal have been moving towards, with Giroud more adept at one touch passing and Walcott also better for a direct style. It was that style that saw Arsenal beat Tottenham, and with Özil they'll only become better at it: he has the vision, pace and passing ability to make Arsenal more devastating on the break. Against teams that don't allow as much space, Özil is still extremely effective, because he creates space both with movement, and with passing.
So, yes, the signing of Mesut Özil is a tremendous upgrade. It wasn't exactly a position of need, per se, but adding to the creativity of the side was a major requirement for Arsene Wenger, and is evident in the players he was linked with--Luis Suarez, Özil, Wayne Rooney and Angel Di Maria. That Wenger pulled out for a move for Higuain is telling; the Argentinian isn't much of a creator, and wouldn't solve Arsenal's issue of being too one-dimensional. Now, Arsenal have a second, world-class dimension, and all teams need that.