Above all I would insert a second theme which is softer, less intimidating, tranquil etc. to oppose this theme. Before doing that you might want to repeat the last 4 measures again, this time with some brass to make it sound broader (or more epic so to say, because most people seem to favour that word here) and to introduce some instruments (brass in this case).
The vocals tremble a bit, is that in your original file as well? you might want to check that out.
For that second theme: maybe reduce the strings to a background, on the beat chord striking fashion in staccato (not pizzicato though) and very lightly, but still a bit building up to something (especially harmonically, not in volume). A pizzicato part, I think you'd better save that for later on because it gives a beautifull relaxing, calm, sweet and innocent sound to it if applied rightly and for that to work, I think the right mood has to be set very firmly. That way the contrast would be at its greatest within the realms of this kind of music. Keep things very tonal throughout, or else change this first part as well to introduce some of the 'strange' sounds you would apply later on.
This (hypothetical) second theme could use a more extended and elaborated melody contrasting the first one, and to make it very lyrical you could use woodwinds. A lyrical melody contrasting (almost battling with) the tension-building strings (very lightly as I said, avoid low registers at first) would work very well there. All between piano-mezzoforte, so it will contrast (again, contrast contrast contrast :P) with the forte section(s) you already wrote. Oh yea don't get the vocals involved in that second theme at first. Later you could experiment with combining the 2nd theme with the vocals in a way they were in the 1st theme, so you could switch between themes, making them interact with eachother, building up to the finale etc.
An obvious modulation could do wonders to extend a finale, but if you do it in the dominating melodical sections, modulate gently to something else.
Also, listen to some of the game and film music on this site (especially the ones that are like your own), and maybe try to leave a comment with things you liked/didnt like and how you would change it. It helps making you think about the subject apart from the actual writing. It might very well inspire you and lift your block ;)
One last thought: harp!