It's really quiet. In fact, it peaks at -10~-7dB.
The pacing is okay, but it's not going to be a meaningful listen. As much as you want to make it ambient, ambient doesn't necessarily mean background music, but this does sound like background music. See if you can find a way to put some more interesting textures into the arrangement, rather than letting your sub bass and nature effects carry the whole song on their own.
When I read ambient, I was expecting lush pads, which did not show up. Maybe it would be a good idea to audition some pad samples.
As far as I'm concerned, the first real lead is at 1:31. Right now, it's bleeding into the background because it's too quiet. Try bumping it up about 4~5dB and boosting at the 1500, 3000, and 6000Hz ranges a little bit with peaking bands to bring out the presence of the lead. Also, try lightly high passing the sub bass, just so it isn't so 'boomy'.
A good example of an ambient section in a song would be this one at 2:03 - 2:56. It does not mean drums are necessary, but they would liven things up a bit.
In other words, this particular version wouldn't make it on OCR because of these reasons:
ARRANGEMENT / INTERPRETATION
[X] Too liberal --- Possibly, due to the long sustained pad-like 'drones'
PRODUCTION
[X] Too quiet --- Needs a volume bump of about 5 dB
[X] Low-quality samples --- The tones are not quite nailed, IMO
[X] Mixing is muddy --- Possibly too much low end reverb, and sub bass is a bit loud compared to other instruments
STRUCTURE
[X] Not enough changes in sounds (eg. static texture, not dynamic enough)
[X] Pace too plodding --- Even for ambient.
[X] Too repetitive --- Yes, even for ambient.