It really started with the Felt 3 albums with Murs but you can start with Skelethon from 2012 and work your way down from there (The Impossible Kid from 2016 is )What albums are these that Aesop produced?
I loved El-P both lyricaly and production wise during the Co Flo days, his Def Jux day is when he lost me lyrically. He was doing way too much. Fantastic Damage is a hard listen, when I listen to it nowadays I think, "What the hell was I thinking liking this?!" Some of the beats are good on that tho. And I like a lot of his production during the Def Jux days, especially stuff he did for Mr. Lif and Cage. Since Def Jux has gone under I like his rhymes more, not as much as the Co Flow days but he improved from his overly complicated shyt during Def Jux. But post Def Jux he seems to be getting worse and worse production wise. As some have said, all the songs sound the same now. I can't distinguish them sometimes or just don't care to.
Basically, he has had a lot of ups and downs both lyrically and production wise throughout his career. I haven't even listened to RTJ4, its not a priority but I'm sure I will get to it eventually.
To me, he's got the atmospheric, yet thumping sound El used to do and at the same time the frantic, almost genre-bending but definitely rooted in hiphop sound El is trying to do now, down pat.
He's even made his lyrics more accessible than ever so he's far easier to digest than he used to be.