One who makes adverse comments
faultfinder, carper, caviler, censor, censurer, quibbler, nitpicker, pettifogger, blamer, detractor, slanderer, maligner, complainer, doubter, nagger, fretter, scolder, disapprover, defamer, disparager, captious critic, Monday morning quarterback*, mudslinger*, knocker*, panner*, basher*.
Antonyms praiser, believer*, supporter.
One who endeavors to interpret and judge
commentator, analyst, analyzer, connoisseur, reviewer, cartoonist, caricaturist, expert, judge, authority, pundit, diagnostic, annotator, master, evaluator, editor, blurb writer; see also connoisseur, examiner, scholar 2.