Shifting system is completely different and I find easier to use from the hoods and harder to shift from the drops which I hardly ever use since the hoods can be more aero and more comfortable. Assuming 11sp-11sp from what I've read you should be able to use current shimano wheels and cassette with no trouble, of course if going from 11sp shimano to 12sp campy you'll need different wheels, Shimano 12sp is getting a different hub design though I've heard the cassette may be backwards compatible to old wheels, I'd assume that means only to 11sp wheels which had a wider cassette body.