I know you like the centered cactus and want to maintain the aspect ratio here, but I think you can gain a lot by cropping some of the bottom off.
As it sits, the brush in the foreground competes for attention with the cactus. Use the same aspect ratio and crop some from the bottom. Move the selection around until you get the cactus where you want it in the frame.
I think you'll like it better, and it also won't look quite so dark.