To be honest. If you have never played d3 please play the story it has a good story line.
It is like diablo 2 you grind to find gear and what not. However I like d3 on the switch I have it for the computer as wel and would sooner play it on the switch.
I enjoy playing on and offline. classes are different however just like diablo 2 they all have their own builds. Many many builds out for each char.
The big question is do you like a tank or dps. All the classes are fun. I personally love the dh have loved it since release. But on the same token the barb is a fun char to play as well as the sader.
I have never played a necro on diablo 3 yet but have maxed every other char on the computer. Again it is all on your play style