List down the episode ID of episodes aired in 2008 with 5 stars and below.
aired in 2008 refers to air_date LIKE '2008%'; 5 stars and below refers to stars < 5
SELECT DISTINCT T1.episode_id FROM Episode AS T1 INNER JOIN Vote AS T2 ON T2.episode_id = T1.episode_id WHERE SUBSTR(T1.air_date, 1, 4) = '2008' AND T2.stars < 5;