Totally agree, he has been probably our second best player this season, sometimes i think that he might hold onto the ball a split second too long but he has stopped so many counter attacks this season and has been our unsung hero this campaign, is possession he's as good as anyone and has shown that we don't need to bring in a defensive midfielder, he is definately the best defensive midfielder in the premier league, his defensive play at corners also doesn't get enough credit, the amount of vital times he has headed the ball away is outstanding.
I know what you mean, we play a dynamic formation that requires great attention and total awareness of each other. If there are just small inconsistencies within the team, it will play badly. We've suffered over the years because we've lost players and had to start over again. We've had the perfect players to play this kind of tactical formation - Cesc, Hleb, Nasri, Flamini but we've had to start all over again. Song is getting better with every season. But we badly need stability in our midfield to make it work. If we keep the same midfield of Song, Arteta and Rosicky fit most of the season and they don't suffer terrible injuries/loss of form, then we should start well and mount some challenge. Adding 1 or 2 players shouldn't be too problematic and enhance the team.
