is the language the author uses in East of Eden mostly plain, concise, or strong

Steinbeck is is never overly colourful with his language. His descriptions are economical yet lyrical. He establishes a sense of intimacy with the reader by using language that is familiar. He tends to rely on simple figurative language to communicate.His prose flows nicely understating his meanings rather than overstating them. Of this novel Steinbeck wrote that he was trying "to keep in an extremely low pitch and to let the reader furnish the emotion." Letting the reader discover emotion rather than imposing it upon him or her further attaches an intimacy between the characters and the reader.

There is another separate detailed essay on this if you like. Just follow:

https://sites.google.com/site/northeastofeden12/style