"Chicken is good."
(1) Single statement
치킨이 좋아요 = (In my opinion) the chicken is good--> (저는) 치킨이 좋아요.
By inference, "I like the chicken."
(2) Open statement [Introducing a topic for discussion]
치킨은 좋아요 = 치킨은 (치킨이) 좋아요 / 치킨이는 좋아요 [Subject ellipsis / abstraction] = Speaking of the chicken, it is good (*but ...)
By inference, "I like the chicken (but...)."
*The topic tag also carries a subtle sense of contrast.