Billy Crystal is always a welcome presence on screen. In his last film, 2019’s “Standing Up, Falling Down,” he played a quirky dermatologist helping a comedian get out of a rut. In “Here Today,” which Crystal wrote and directed (his first feature in 20 years), the tables are turned; he stars as a comedy writer who learns to love life again thanks to an unlikely friendship. A takeoff on the Alan Zweibel short story “The Prize,” Crystal writes himself a honey of a role that he performs with his signature charm and wit. But he seems to have forgotten to write any of the other roles with the same depth, which is a darn shame.