They've mentioned several times which artist was the definitive inspiration and they both said it was Maurice Noble, famous for designing the backgrounds for a lot of Chuck Jones shorts. I can't recommend this book enough: https://www.amazon.com/-/es/Tod-Polson/dp/1452102945
If you get soaked with Noble's body of work you can definitely see that they continue to pursue his style, even though the color rendering is different from the 2 previous games. I am very psyched to watch what they did, honestly I don't get all the hate that the art style got. We, as fans, should be rejoicing with joy that most of the original team is back (even though of course we all wanted Tim to be part of this). I get that not a lot of people loved the art of Broken Age but c'mon a lot of us waited so many years for this to actually exist so I will quote Stimpy: "Happy, Happy, Joy, Joy!"