For a literal, physical description:
* Dull: This is the most general opposite, meaning lacking shine or luster.
* Tarnished: Implies a loss of shine due to age or wear.
* Grimy: Suggests a surface covered in dirt or grime, obscuring any shine.
* Dusty: Refers to a surface covered in a layer of dust, making it appear dull.
* Faded: Indicates a loss of vibrancy, including shine.
For a metaphorical or figurative description:
* Dim: This suggests a lack of brightness or brilliance.
* Uninspired: Implies a lack of excitement or passion.
* Mediocre: Refers to something average or unremarkable.
* Ordinary: Means something common or unremarkable.
* Lackluster: Indicates a lack of energy or enthusiasm.
The best opposite will depend on the specific meaning of "gleaming" in the context you're using it.