In each of the seasons, the episodes become more and more interesting down the line.
In each of the seasons, the episodes become worth watching more and more as they progress.
ご質問ありがとうございます。
① "In each of the seasons,"＝「各シーズンで」
"the episodes become more and more interesting down the line."＝「エピソードは後になるほど、ドンドン面白くなっていくよ。」
② （同上）
"the episodes become worth watching more and more as they progress."＝「エピソードは進めば進むほど見る価値が増すよ。」
ご参考に。
アメリカ合衆国 
