This is solid. As far as arrangement goes I think you could have built up the part where the kick comes in around one minute. I like how you bring back the same main theme. The ebb and flow is nice. However around the 3 minute mark it seems like you've been hammering the same theme for a while now. Maybe try hitting a variation on the main theme towards the end to keep things familiar but still fresh if that makes sense.
Mix concerns: The bass seems a little bit busy, it's hard for my ear to keep up the low end. The kick is clear and sounds good but it doesn't really sound like it is being supported by the bass. The random sample panned right around 2 minutes sticks out a little much. You could try putting some reverb on it to move it further back in the mix. Either way it seems a bit loud in the mix.
All in all it sounds really good. The volume cuts out a little at 2:35. Are you using Ableton? I've had what I believe is the same issue with Live 8 and was wondering why this artifact occurs when rendering (or maybe its my fault who knows).
