The show and characters have just become repetitive. It's the same every week and the way they make every case 'personal' is getting tiresome. It was never this way, each character would have one or two 'big' episodes per season where they got some personal development and the rest of the time it was working together to beat the bad guys. Now they just spend most of the time digging someone out of a hole.
And the characters are boxed in. Atwater does nothing but do undercover buys (usually badly) until he needs to be wheeled out for his black v blue episode, Ruzek does SFA until he's needed to fuck something up, Halstead, well look at his 'big heart' he fucks up and everyone is 'awwww Halstead just cares too much.' Burgess sticks pictures on a board until low and behold she gets a story that involves her tragic love life, and Upton well she's in everything pontificating, snarking, stalking halstead and smirking her way through facilitating murders, planting evidence & pretending her shit doesn't stink. Rojas is just there, not really bringing much and seems to be destined to prop up her housemate and make her seem like she has friends.
And I was never an Erin fan, but I will put my hand up now and say, the grass was not greener on the other side.