(Note - I review pretty harshly, so don't take a low score personally! I don't vote harshly.)
First, I don't think this is really ambient - it's closer to techno. But I won't dock you points for that.
It's very tough for me to give good critique about this song, for some reason. The honest truth is that it's not really clicking with me, for some reason. I wanted more out of the climax, for some reason.
I think that the main thing is that the melody at the climax of the song is not very strong, so the buildup is kind of a let down. You could also just make the build up a little stronger - that might help a little bit too, if you want to fake it ;-) (nothing wrong with that).
I do like the incorporation of the acoustic guitar into the song! Definitely keep that up :-) This song is a good start; keep working at it.