This is very good. The changes in mood, etc seem random-- like a movie score but with no visuals to match the changes in mood to, so the effect is a little confusing. It would work better as a stand-alone piece of music if the mood moved in a particular direction, instead of jumping around a bit like it does. I also agree that it needs more in the low end. Doesn't really need more notes than you're providing with the bass guitar (at least not very many more), but maybe something with more sustain, like a nice interesting synth. Imagine listening to this in a movie theatre ... you would want your seat to be almost shaking, to feel the intensity in your chest. In other words, needs more bass. :) And of course, it needs an ending.
Great piece though, you definitely know what you are doing.