Interesting topic!
My previous bike was a Thunderbird LT, the quintessential British cruiser and Harley beater (I also have a Road King which I really like so am not anti Harley). I loved the Thunderbird and got a great buzz riding it (even slowly round town) and what a mile eater on the highway!
So why change to the new Rocket? In my case it was age and arthritis, the T-Bird was just getting too heavy in every way, the clutch was too stiff it killed my left hand, no cruise control killed my right hand and the bike was just too difficult to maneuver around. Final straw, the tubed tires, having spent a long evening at the side of the road with a flat waiting for a breakdown truck finished me off!
The Rocket fixed all the above problems and still gives me a big imposing cruiser, feet forward riding position, it is almost an automatic (with the quick shifter) has cruise control, tubeless tires and is nearly 70 kg lighter that the T-Bird (the much lower centre of gravity and lighter more balanced front end make it seem lighter still). You can ride it slow and easy like a cruiser and fling it through the twisties if you want. And yes, seeing the faces on other people when you tell them the engine size is a blast!
There is only one aspect of the bike that doesn't do it for me and that's the look (yes, I know that's why most of you bought it!!) and maybe I'm in a minority of one here, but I am working hard to change the look to that of a bagger / tourer since that's what I want (I don't like the Corbin look, it makes the bike look way too heavy, not to mention the cost!). I will post pics when it's finished and most of you won't like it but I don't care!