I think the layout is only a portion of the problem - the overall content of in each page is lacking, so even if you do a fantastic layout, a fantastic layout of mediocre sketches is always going to appear worse then a crap layout of awesome sketches.
Rather than give specific feedback I would just spend a lot of time browsing other peoples portfolios and work to give yourself a comparison. See who gets featured on Coroflot and what their work looks like and how your stuff is stacking up, and then figure out how you need to rework or revamp your projects to bring the quality level up.