WordNet sense 1 (being or affecting or concerned with a surface; not deep or penetrating emotionally or intellectually):

superficial

WordNet sense 2 (requiring or apparently requiring no effort):

effortless

WordNet sense 3 (expressing yourself readily, clearly, effectively):

eloquent, fluent, silver, silver-tongued, smooth-spoken

WordNet sense 4 (expressing yourself easily or characterized by clear expressive language):

articulate, articulate