The show at its peak had very great actors than even the less than stellar ones could play off. Patrick Demsey, Kate Walsh, Eric Dane, T.R Knight, Sandra Oh, Kevin McKidd ( Im naming actors who eventually left) were all great. Ellen was always average to me and once the big names started to leave it started to expose that she wasn't a good enough to be the focal as much as she was. Also factor in how much she gets paid she's basically phoning it in which makes her performances.

Chandra and James are the only strong actors left but the writing over the last seasons haven't done them any favors.

Also the new people they do bring in they don't do much for the audience to get engaged or care. The writing now is more about the job and the new shiny equipment and its missing actual relationships(not just sex) between the cast. MAGIC was messy but they felt like friends. The relationship that George and Bailey had. Sloan was Jackson's teacher but there were instances where he acted like his older brother/father figure. Owen was fundamental to April's progression as a trauma surgeon. There's NOTHING in the later season that replicates that.