General Negativity:
* Dismal
* Gloomy
* Depressing
* Desolate
* Somber
* Cheerless
* Hopeless
* Grim
* Unpromising
For Landscapes:
* Barren
* Desolate
* Stark
* Arid
For Prospects:
* Unfavorable
* Uninspiring
* Discouraging
* Pessimistic
For Mood:
* Melancholy
* Morose
* Dejected
The best synonym to use will depend on the specific meaning you want to convey.