When you're writing/recording orchestral music, you need to imagine how each instrument would play their parts. This piece is clearly the result of a piano/keyboard-player playing each instrument like he would play the piano. And the result is a rather static, synthetically sounding bowl of musical "spaghetti". There are several ways to make this a better performance. First of all you could
get some better sounding samples, but more importantly you need to learn how to work with Expression, Velocity and Dynamics. Expression can be added either by changing the master volume of a track by automation or through designated MIDI controller parameters like CC#11 (the standard for most professional sample libraries). What expression does is that it gives you the possibility to control the attack and volume of an instrument. Most humanly played instruments don't start playing at max-volume, because usually the instruments want to blend in and not take center stage all the time. Changing the velocities of individual notes ensures that it gets a "human touch", since no player in the world can play at the exact same velocity throughout a tune. Take your harp for example, that is a fine example of something that is almost impossible for a harpist to play. Those very fast staccatos without much change in velocity would make any player's fingers bleed in no time! And your violins sound like they've been recorded using a sustain pedal which is totally impossible in the real world! For violins in particular velocity and expression are of utmost importance.
Consider these two quick examples I've made here:18 violins - no expression18 violins - expressive
This is the exact same melody line. For the latter version I've added expression and adjusted the individual velocities. Although not perfect it sounds a lot less synthesized than the first one.
Changing the dynamics of the orchestra keeps the listener interested. Some parts should be played lower and some parts louder, so that it doesn't become a "wall of sound".
Sorry for using my own music as an example, but listen to this: An adventurous piece using dynamics
It starts pretty low key and builds up continuously. That's changing dynamics. It's a loop - and mp3 doesn't handle that very well, so it'll have a small gap at the end. Sorry about that.
Anyway, your piece is not bad as such. Nice melodies and nice thematic development!
Take my advice with a grain of salt - I'm simply just trying to give you a few pointers on how to improve your work! :-)