Hi Ben, I think you have a lot of good ideas here that can be better executed... I noticed that there wasn't legato playing in any of the phrases... using cc controllers, depending on what orchestral library you're using, you can create more fluid lines...
Also, I'd like to add that you captured the feel for that type of composition for action games with your harmonies and rhythms...
Compostion is a life long study, so if you don't get great reviews in some of your first pieces don't get discouraged...
I would suggest as a way of hands on learning orchestration, get yourself a piano copy of "pictures at an exhibition" and then get the orchestral score by Ravel.. analyze each piece, learn the harmony, learn the melody at the piano first, and then look at what Ravel would do to convert the piano score into an orchestral piece... That would give you a good understanding of converting 'piano chords" into orchestral writing...
Now I'm assuming that you have a thorough knowledge of all the instruments of the orchestra... If you don't, you can always get orchestration books that will teach you about ranges and where the instruments sound best as you analyze the piece... But I think you learn better by being able to refer to a piece of music, as opposed to just learning things as a dry scholastic exercise... Pictures at an exhibition is something you can wrap your head around easily... Anyway, keep writing and remember that each gig is an opportunity to learn something...