Zhè bù diànyǐng tài chénmèn le, wǒ chàdiǎn shuìzháo le.
This movie was so dull, I almost fell asleep.
Tips
usage
沉闷 has three related uses: weather (stuffy/oppressive before a storm), mood (depressed/gloomy), and sound (muffled/dull like distant thunder). All share a sense of heaviness and suppression.