If you're flying out on Delta, you'll be flying out of the Concourse. The lounges there aren't much to write home about. Better bet would be to use the Asiana/KAL lounges in the Main terminal and then take the train to the concourse.
That said, the Asiana/KAL lounges are solid if unspectacular. The food is ok (not replenished often enough), but there's enough space to sit and relax in some peace and quiet.