Hey man,
Pretty cool intro you have here. I find it kinda hard to comment on an introduction though; it's hard to say I like this or don't like that when I can't explore the whole vision. But as it stands, here's some thoughts:
I like the sense of drama you're creating. You have some moments that are lush and striking, like when you added the harp texture with the violin melody, soon to be taken by the winds. I also like how you're taking advantage of different colors the orchestra has to offer, like when the trumpets played with the opening triplet motif in the waltz section.
Your piece also felt cohesive. You transitioned pretty well to different sections, as it never felt like a mash up of ideas.
However, overall I felt like you took your ideas and just repeated them into the ground. The section at bar 20 felt obnoxiously long, and even though you did change the chords they were playing, it wasn't until bar 46 that we got some reprieve with the added suspense with the trombones (cool touch though). Same with the theme I mentioned with the harp and string melody. I love the progression, the descending bass was really powerful. I just think you stay too long on an idea without giving it variation. The overall vibe of block chords can be tiresome to the listener, so maybe think about how you'd like to make your already nice chord progressions a bit more varied from block chords. You've got the whole orchestra!
You do afterwards present that theme in an almost double time fashion which was nice, and then I liked the major key that followed, but we were yet again met with more block chords. I feel like you could maybe get away with that, but with the full color palette of the orchestra at your disposal, some variation in tone color would help. I wasn't too into the waltz theme, but like I mentioned earlier, hearing snares and trumpets play over a lighter tonal character was pleasant.
The brooding dark string chords at the end were awesome. It definitely was a suspenseful cliffhanger and a very fitting end to what I'm excited to hear next.
In general, I think your themes were present throughout and made use of compositional technique, but just reconsider how you're using repeated sections. Great start so far, it's daring to try your hand at using a full orchestra.
Also, I echo Mr. Tom. I think writing smaller pieces to practice counterpoint and what the instruments are fully capable of is paramount in getting better at your craft! Keep up the good work