TOS and TNG will both maintain their legendary status IMHO. The reason is that they are Shakespearean. Both series are presented very theatrically - the acting is often broad and dialog is clearly enunciated. Many of the stories are updated versons of Shakespeare plays and the characters regularly quote dialog from the bard.
Shakespeare is timeless and universal - the works are over 400 years old, so TOS and TNG should both be relatable for a while yet!
Shakespeare is timeless and universal - the works are over 400 years old, so TOS and TNG should both be relatable for a while yet!