indifferent(mediocre, usually used negatively) adjective [UK: ɪn.ˈdɪ.frənt] [US: ˌɪn.ˈdɪ.frənt]
lackluster(not exceptional; not worthy of special merit, attention, or interest; having no vitality) adjective [UK: ˈlæ.ˌklə.stə(r)] [US: ˈlæ.ˌklə.stər]
mediocre(having no peculiar or outstanding features) adjective [UK: ˌmiː.dɪ.ˈəʊkə(r)] [US: ˌmiː.dɪˈo.ʊkə(r)]