Not a City fan, but people should understand that Pellegrini is a brilliant manager.
That Real Madrid team wasn't even close to the quality of the current Madrid team, on paper. No Ozil, no Modric, no Di Maria, no Khedira, but they still finished on 96 points which was higher than Mourinho's first season. They scored 102 goals and had a +67 goal difference. Mourinho signed Ozil, Khedira, and Di Maria in his first season and finished on less points, same number of goals scored, and +69 goal difference.
I would go as far as saying that his Real Madrid team wasn't quite as good on paper as the current Manchester City team. He also obviously did great things at Villareal and has been successful at Malaga. Plus his teams usually play great football.
The only criticism I would have is that I think Manchester City are more in need of a manager who can instill a winning mentality throughout the club, someone like Jupp Heynkes or Fabio Capello would be better imo, but Pellegrini will set up a team to play exciting football. He will be successful, I'm sure of it.
Be thankful that you aren't getting Moyes.