Don't think his "new" game suits playing upfront on his own, especially against a good defence/a team who keeps the ball better than us. He's not physical enough, most of the time rather than challenging for a header about he spins behind in the hope that the opposition misses the ball. His press game has gone and so has his playing on the shoulder, he just doesn't want to work hard at the moment, probably due to fear of injury. His dropping deep is ineffective as he's not going to drop deep to get the ball, look up and spray it out wide then bust a gut to get into the box. Instead, he just drops deep turns and tries to do a Maradona vs England every time.
Pellegrini's tactics are just at fault seeing as how much work he has our wide players do, leaving Aguero isolated because the wide outlets are closer to Hart than they are to him when he receives the ball.