이것은 좋은 선물이에요. 하지만 못 받겠어요.
이것은 좋은 선물이기는 해요. 하지만 못 받겠어요.
As you know, the expression "-기는 하다" is usually used when saying that speaker has acknowledged/accepted/recognized the fact that it is really/indeed true.
But, this expression has a nuance that speaker doesn't want to admit the fact, but the speaker must admit it. In other words, it tells the speaker's dislike or disapproval about it.
Whereas, "이것은 좋은 선물이다" is a statement, so this sentence doesn't have the nuance of the speaker's dislike or disapproval.