This isn't ambient
This might be a better fit in the classical section.
But regardless, I think that this is a really well-constructed and catchy piece.
The only thing I can really suggest is to make greater use of melody, particularly after the 3-minute mark when the piece nears its conclusion and you have all of these dramatic chords. If you had had a melody playing above them at the same time, that would've been simply sublime. I know that at 3:15 you had something kinda melody-like playing up high (broken chords basically), but I think that you could've put another, louder, slower melody even higher than that for a truly dramatic effect.
Other than that, hmm... well, one more thing: the sound of the guitar(s) here is ok, but it sounds a little too sharp and shrill. Something a little softer sounding, if possible, would be better.