All this needs is dynamics

Melodically and harmonically, this song is pretty good. However, without dynamic changes, it sounds stale.

I would also try to bring out the drums and vary up the rhythm a bit more too.

Lastly, I would use different samples, or soften/vary the attack on the strings because everything seems to be playing in basic sustain mode.

Those are the main things that stick out for me. But like I said, the melody is fine.