For the price for five speakers and a small sub they don't lack anything too badly. In fact, I was really pleasantly surprised by the sound of this setup! My opinion is that the sub would be the first upgrade, the satellites sound pretty amazing in their limited range you won't need a sub right away but since you found this forum... lets just say enjoy your hobby.
If you're willing to spend the extra $ the energy CB-5's and CC-5 are a solid upgrade to the take classic. You can demo them in just about any Best Buy with a Magnolia Center. Just don't get suckered in to $200/pair MSRP. I bought a brand new pair ofCB-10's for that on sale.