Alright, here's some things I heard.
1) I think the overall arrangement is solid and works well, I wouldn't mess with this.
2) In the first 10 seconds, It sounds like you're using one sample and trying to get it to do two different things. If you want that opening to sound as if it's being played by one instrument, then I'd either choose a different instrument (like piano, or some mallet instrument, or maybe a harp...) or get a better sample. If you're going for two instruments, then I'd replace what you're using for the accompaniment sound with something different.
3) Overall, the drums sound good, I'd leave those alone for now. I like that they're not too heavy, they fit in well with the general feel. The bass that kicks in at 1:05 and 2:57 is also good =] (Though maybe a little overpowering, but I think that's more an issue with the other instruments being a bit underwhelming)
4) The "electric guitar" that starts at 1:35 (and 3:32), I'd scrap it. It sounds really not so great compared to what's going on around it. You could maybe try replacing it with some brass instead, I think even fake electro brass or lo-fi brass would work well (or at least better than that current sound =[). Play around with it.
5) In general, your melodic lines sound pretty stiff. A little inflection/humanization would go a long way to make those parts sound more interesting. They could also stand to be brought out more, I was sometimes struggling to hear the melodic bits amidst everything else. They weren't completely lost, they could just stand to be more prominent.
6) The last thing I'll say is that the build up around 2:44 needs to be bigger. What you have can work, it just needs to get louder for the silence to be even more effective. I'd compare the builds peak volume level with the volume level right after the silence (they should be about the same, or at least closer than they are). I'd also either a) cut off the lingering delay effects and make sure everything cuts off uniformly there, or let the silence linger just a bit longer if you want to go for a fake ending kind of thing.
There's my 2 err... 6 cents. Hope that helps! I think what you've got could be really awesome (and is already pretty awesome), and I can hear where you're trying to go with it. Just give some TLC to the non-synth/non-percussion instruments =]