IMO, it's completely fine to rate a soundtrack simply based on how it made you feel, personally. There's no reviewing art completely "objectively", it'd be a bit boring if that was possible ;)
If an ambient track's compositional elements don't engage you, there's nothing wrong with giving a lower score there. Someone else, who's a huge ambient enthusiast, may feel very differently about the track and give a higher score, and vice versa in genres that you are more well versed in.
We all have our preferences, but in the end, those will (hopefully) balance each other out and what we're left with is the music that resonated the most with us floating to the top. I think that's better than everyone trying to become 100% accurate, objective Art Robots who rate what they hear based on some factual musical checklist.