So...this was awesome.
Seeming as everyone else has said this is fine as it is, I'm going to listen to it as if it's a finished piece.
Nice start; it's simple, but you can tell it's going to build up into something huge.
The staccato cellos (I think?) at 0:23 are nicely done, just giving it that extra edge of pace.
The sudden buildup at 0:45 is again, very well done. Simple but epic melody, nice underlying chords.
The part around 1:10 where it kind of goes to build up into something huge again, before dropping down to almost nothing is possibly my favourite part. Because it builds the anticipation like nothing else.
The ending is abrupt, but fittingly so.
If this is the UNFINISHED version? I'd hate to see what kind of mastery you come up with when you think it's done. I think you're possibly being too critical of your own work; you can't think of what to do because there's nothing else to be done. You could easily leave it as it is. I refer to your average scores to lend a credence to this. Very nicely done.