Typically use WordNet’s synsets and hierarchies to acquire opinion words
Start with a small seed set of opinion words.
Use the set to search for synonyms and antonyms in WordNet (Hu and Liu, KDD-04; Kim and Hovy, COLING-04).
Manual inspection may be used afterward.
Use additional information (e.g., glosses) from WordNet (Andreevskaia and Bergler, EACL-06) and learning (Esuti and Sebastiani, CIKM-05).
Weakness of the approach: Do not find context dependent opinion words, e.g., small, long, fast.