Decent work, but it could use some improvement. The loop throughout the entire piece gets pretty repetitive and dissonant at times. If you want to repeat it throughout, try adding variations or modifying the voice to match the melodic content of the main melody. Also make sure the main melody is louder or more dominant; the loop should only serve as rhythmic/harmonic support. The piece should also be smoother, with more legato; there were some choppy bits near the end. Overall, it's a nice attempt, but hasn't quite met the peaceful, serene mood yet. Listen to some ambient tracks on newgrounds or sakari-infinity.net, it'll help you get a better feel.