Saw them right after CTA was released at a small venue here in Houston. Maybe 40 people there. Phenomenal, they were young and on FIRE!! Saw them a short time later right when Chicago II was released at the Houston Music Hall. Same thing, just cooking. The rhythm section was a machine. Kath was certainly known for his extraordinary lead playing, but his rhythm playing was also incredible.
Saw them again right after Chicago IV was released, and it was not the same at all. Cetera was playing a fretless, the tightness was missing, and the horn section appeared to be stoned or drunk, very sloppy.
With the loss of Kath (everything he added, voice, energy, playing, etc) they seemed to become complacent. I understand the label was trying to turn them into a pop band backing up Cetera, even suggesting they ditch or limit the horn section
From what I've heard they are playing at a high level once again, although with a lot of new faces.