In the poem "To An Athlete Dying Young" what are some important features
Although I generally do not like sad poems, this has always been one of my favorites. I don't know exactly what you mean by "features" but here are some literary elements in the poem.
In the first line, you see a couple examples of alliteration -- you have both words beginning with "t" and those beginning with "y." Later on, you have "townsmen of a stiller town," with lots of "t" sounds again.
You have personification, as in the place where the night shuts the athlete's eyes and where glory does not stay on fields -- both night and glory are inanimate but are given living characteristics.
Finally, you have synecdoche where a part of a thing is used as a metaphor for the whole -- the foot is on the sill of shade, being used as a metaphor for the whole body.
The most central feature of "To an Athlete Dying Young" is the premise of the poem. The poem suggests that a successful athlete is better off dying young, because the best of life is behind him. The athlete dying young is the lucky athlete.
Irony is used here to treat society's hero worship of athletes. A sad poignancy results from the exposure of a young person's dismal future following an adolescence of local fame. The poem exposes the irony of a society that places so much emphasis on something of so little value, and a society in which so many live vicariously through so few.