I had the exact same thoughts with ambient tracks! They can be very powerful in relation with the environment they're played in, but alone struggle to hold interest as much. I tried to rate them as if I was hearing them in a game, I tried to match it to the scene the creator described.
For composition in ambient tracks, I tried to base it off how immersive and huge the environment felt (as they typically aren't rhythm and melody based so you can't really grade off that.)