I think the reasons I DON'T feel my descriptions are very strong are really two-fold: 1) I can see it, so I expect my readers can, too, and 2) I think we all feel a bit repetitive saying things like, "the man had dark brown hair and blue eyes". There's only so many ways you can write that description before you want to bonk yourself over the head with a hard object.
But consider that there are five senses to use for description:
The chair was dark red.
His hair was jet black.
The sunset shone copper off the water below.
What about using SOUND?
The waves crashed upon the rocky shore, reverberating in my ears.
The chair smelled of mold and dust, having sat unoccupied for more than five years.
His hair felt like silk against my fingertips as I brushed it back from his forehead.
The brine of the seawater filled my mouth, sharp and sour against my tongue.
Okay, this won't win me any Pushcart Prizes, but it'll definitely help exercise my descriptive writing muscles...