What does Nick say is gorgeous about Gatsby in The Great Gatsby?
After saying that Gatsby represents all the things that he detests, Nick says that Gatsby was not so bad. Gatsby is an exception to Nick's pattern of attitude and predilection.
Gatsby is quite literally exceptional in ways that Nick is hard-pressed to directly express. Despite the difficulty of pinning down the qualities that make Gatsby exceptional, Nick makes an effort:
If personality is an unbroken series of successful gestures, then there was something gorgeous about him, some heightened sensitivity to the promises of life.…
It is Gatsby's hope and self-belief that make him exceptional. This self-belief is not exactly the same as confidence. It is wrapped up in a sense of destiny that goes beyond mere confidence. Gatsby's penchant for hope and faith in himself are unique in Nick's experience.
These qualities set Gatsby apart from other people Nick has known, including those discussed in the narrative of the novel.
The "gorgeous" aspect of Gatsby is what leads both to his success and his ultimate failure. He pursues a vision unwaveringly, but that vision includes a degree of idealism that makes it nearly impossible to achieve and certainly impractical. The fact that Gatsby believes so fervently in this vision speaks to an innocence in his character.
He believes in the impossible as possible, in fantasy becoming the basis for reality. This makes him a somewhat poetic figure and one that Nick finds a kinship with, as Nick is also something of a romantic in his own way.