haha - Nice! Sounds like Shinobi if it were a cartoon back in the 80's (and the brass was surprisingly smooth - might I ask what program was used?). That said, my comments on this would be that around 30 seconds or so, I know there are some chords that I was expecting to hear (I listen to this ost regularly lol) but they were missing. Perhaps you could take a simple piano and subtlety slide them in there - as without them it feels rather bare. Also, the drums feel really..compressed (that's the best word I can think of) - but it's most likely just me.
I can't comment much in regards to arrangement, as it's something I'm really weak at. However, I will say that perhaps some additional chords and an arp may go a long way with this; as it's a really short and to the point mix; not allowing much room for expansion if you're simply updating the old track.
That said, was a nice blast of nostalgia for me and it's shaping up to be really neat - lookin' forward to your finished version ACO.