unexceptional vs run-of-the-mill

unexceptional and run-of-the-mill both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unexceptional	No	Yes	No	No
run-of-the-mill	No	Yes	No	No

As adjectives, unexceptional and run-of-the-mill are synonyms defined as:

unexceptional and run-of-the-mill: not special in any way; lacking distinction

Other synonyms of unexceptional include mine run, run-of-the-mine, undistinguished.

unexceptional (adjective)	run-of-the-mill (adjective)
not special in any way; lacking distinction	not special in any way; lacking distinction