I liked it the slow build up from the A section to the more aggressive sounding B section. The only recommendation is to create some variety in the notes, especially the bass. Perhaps an ostinato style, or something of that likeness -- since it can get a tad repetitive. As far as harmony goes, I really recommend just going with what you feel sounds good, and don't focus too much on the I-IV-V-I aspect. It helps you get out of your comfort zone, and really explore your personality as a composer. Overall, nice work.