Pellegrini's always been stuck in an unenviable position when it comes to his standing amongst the supporters. He was for the obvious reasons of who he replaced and how that came about, an unpopular appointment when he came in. The double in his first season helped to bring everyone onside, but last season's on field travails, especially in the early Spring, coupled with the Guardiola stories first surfacing back then, pushed his popularity downwards again. In essence he's been stuck between the memory of Mancini and the shadow of Pep pretty much since his appointment, making it very hard to have any real perspective on the job he has done.
The one thing which can't be denied is that he has handled everything thrown at him with the utmost class and dignity. But personally, I think that to some extent that's just damning him with faint praise. For me the football we played in the 13/14 season was the best i've ever seen City play full stop. I don't think the Premier League at that point had seen a side play with such attacking ferocity and dismantle teams with such ease and effect. If any United team had done that ever they'd be being held up as one of the greatest PL sides ever.
For me with the exception of Pep there really isn't that many managers out there, if there are any, who I'd swap Pellegrini for. Yes he's rubbed some up the wrong way and frustrated many more, myself included at times, but when you look across the Premier League or even across the major leagues in Europe, there's very few currently coaching at the level MP is at.
Personally I hope he doesn't take the Chelsea job. Part of me would've been happy for him a month ago, but having thought about it I'd much rather he went back to Spain. The thought of him at another PL club doesn't do it for me.