I enjoyed the drums. I almost feel like there should be a higher-register lead over it or something. I listened to after the drop a few times; I really like the heavy bass you end up with; I do feel the part of the bass you kept over from the first part could have been a bit different, as now it plays part in call-and-response, and is not just the only bass. I am not sure what IV4 meant by structure, but I would agree that the hardest work ahead of you is turning those great ideas in the WIP into a full song with coherent parts...