depressive, cheerless, gloomy, dismal, sad, grim, joyless, saddening, dark, disconsolate, uncheerful, melancholy, blue, dispiriting, happy.
de-motivating (part of speech: verb)
depressing (part of speech: verb)
dissuading (part of speech: verb)
lowering (part of speech: verb)
boring (part of speech: adjective)