The main difference is that the standard focusing screen is much brighter on the C330s (interchangeable focusing screens are not compatible with previous models). It's a lot easier to use with prism finders. With a C330/C330f, you would have to buy a costly Beattie or Maxwell screen to achieve the same result.
The C330s is slightly lighter than its predecessors. As stated by Jeffrey, it has a little bit more plastic parts. But I feel that overall quality is not compromised: it remains a very rugged camera. No changes sizewise, it's still much bigger than a Rolleiflex.
Apart from that, there are a few cosmetic differences, but nothing to write home about.
Cheers,