Great detailing! Besides the relative size issue, I would say that cast shadows would be helpful. There are lots of forms on the APU that would cast a shadow on to other areas of th machine.
I would get rid of the background, otherwise it's fantastic! But agree with dumbo, you two are way too big compared to the three in front. Heh, and I love the way you did Morpheus and Trinity but Neo is not himself very much...
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