Are you aware you used the same opening 3 notes as 'Also Sprach Zarathustra'?
http://www.youtube.com/watch?v=SLuW-GBaJ8kRather than getting into the iffy side of 'musical borrowing', I suggest emulating it, instead of taking it. It's surprising how 3 notes can make all the difference!
Anyway, your requested feedback:
The pizz. kind of works. It would work better if it was a big pizz chord through the whole string section I reckon. Or maybe because the cellos seem to be already doing something, just from the viola upwards.
The transitions sound fine, but mainly because the actual sections sound quite similar to each other. Which means it works!
If you want to include woodwinds, I'd suggest runs. Really quick passages to add tension in the latter half of the piece. Double the flutes with the violins when they take the melody. In the little ostinato which starts at 1.52, add a bassoon adding accompaniment underneath with the same rhythm.
There's some suggestions!
For other feeedback:
Some of the brass need a bit more attack. They sound pretty good, but they also sound like how the strings work in terms of adsr (attack, decay, sustain, release). Brass tend to be a bit more parpy. Even in the quiet registers, there is an ever-so-slight parp quality to it. Some of your brass don't seem to have this, so maybe raise the attack up slightly.
I think the more exciting section starting at 1.52 would work well if some brass staccato was layered over it as it developed. When it gets to about 2.40, it feels more anticlimactic, instead of a big climax.
Quite nice overall though. I think those pointers will turn it into something great!