I like it

Hey nice man this sounds like exactly what I need for a sad part in a video i'm making would you mind if I use it.

Great

So beautiful! ^.^

"Calm"

It seems calm and subtle more than sorrowful, but it depends on the listener ;-)
I'm no music theorist, but this piece was very nice, and it pulled a few of my heartstrings listening to it.

Truly moving

this was truly sad, moving so gently... it moved me a great deal.

I know this was just supposed to be a piano piece, but I can imagine this piece with a gentle rain, viola/flute weaving in and out of the piano.

So gentle.

This is a really good piece. 5/5 from me LfunkeyA, again this song so deserves to be in Classical, not Misc.

Not too bad, but a few issues

What you've got isn't terrible, but there are several things which you could do to improve it. Firstly, add some structure. A simple Binary or Ternary form (e.g. AB or ABA, probably Ternary would be best) would add a lot to the piece. For example, expand into a slightly 'fuller' B section, with the chords filled out in the right hand, and return to the original idea to close. Another point is to avoid thirds in the bass, as it tends to sound muddy, especially in a quiet piece, and especially when they are used so regularly. Either spread the chord, use 6ths or 10ths instead, or raise them an octave or two. Finally, record and play it yourself, if possible! The music is sapped of emotion by the robotic, perfect playing style. Play rubarto, and add more dynamic variation!

Aside from this, you have the makings of a pretty good piece here. Don't give up on it, but attempt to expand it and make it better, and post your results.