It's actually very easy as you get the hang on, as basically the only thing that doesn't get dictated by your cooldowns is the regular dot, and that one has the same cooldown as merciless/annihilate.
Then you just have to take into account your focus, which once you practice a bit you will know how to deal with it, and it's pretty much a static rotation.
Carnage/Combat is easier to begin with, but harder to master, as it requires much more APM than watchman/annihilation.
About being harder than other classes, i don't know. I had played merc, powertech, sorc, sin, sniper, and none of them are harder than a marauder.