His poetry has a dim, obscure quality that makes it hard to grasp.
Tips
register
Literary register. Lu Xun opens 《故乡》 ("Hometown") with 时候既然是深冬;渐近故乡时,天气又阴晦了 — that line is the canonical encounter most Chinese readers have with 阴晦, so the word still carries a Lu-Xun-ish melancholy in modern writing.
usage
Two senses: literal (overcast weather) and figurative (gloomy mood / obscure meaning). For everyday "cloudy" speech use 阴天 instead.