Well it's interesting...
If the title of this work was "Opus 10" (and not "Newborn Prince"), and perhaps also your nick wasn't "LostSamurai"... I mean, withouth any references, this music could mean anything to me. OK, something epic, because of the fanfares, but any thing.
In fact you say you start with "a film in my head"... So there is a clear purpose in this music. That's why, without that "film" you imagine it doesn't work the best. That's whta I was trying to say with "a music by itself". I know that if you're writing a music for a film everything is different (I have done it with some silent films), and in this case the structure of the work has to be altered sometimes.
But for a piece of music and nothing else, it will be better with a structure.
Mm... perhaps that's a benefit to looking at music multi-purposely, but even then, working with guidelines provided is always helpful.
I'm with Luis on the chord progression part. I do hear it change occasionally, but it does need to change, regardless if it was a sound library exploration. I hear (I, VI, iv, I), a lot of the time; sometimes I hear VIM7.
For a game it would largely depend on what it was for. If it was for a player-controlled cutscene, perhaps the bigger sounds were a bit too big in contrast, as the player should treat it as an atmosphere. If it was a regular cutscene, then it definitely needs more variation or change. If it were in a level, I'm not sure; it has its pros and cons.
The major purpose in an exercise like this, I think, is working with what you have, but not to the point where it dominates over form and orchestration.
It's nice, and I get a sort of Fire Emblem feel when listening, but it does start to become stereotypically flatlined after a while.
Usually when I start on a piece I picture a film in my head, just something random. And think what part of this imaginable movie can I express in this piece. Since music seems to follow along with what the characters are doing or feeling on screen, I noticed the music changes along with each dialogue, expression, or gesture which is what I tried to do here...I just kept that to myself haha.
I tried to portray the birth of a new prince, which is why I used the Oboe among the brass and strings. The trumpets was a sign of the kingdom celebrating said prince. I know it sounds funny...
You know what? It depends on what you want from you music.
Is this just a "study" to try some sounds? Then OK, it's perect.
Is this a music to go with some scene of a game or similar? (I tell you this because it seems you are fond of that). Then probably it's fine becase although it's repetitive, you work variation with instruments.
Is this a music by itself? A "piece of music" to listen to with no images and that? Then it becomes monotonous. The idea is good, but the same progresion (I-bVI-IVm-I... I think) over and over becomes tiring. If you take two different (contrasting) ideas you can work with them and built pieces with coherency and variation: ABAB, AABA, etc...
Anyway, it sounds nice.