UPDATE: Apple changed my Watch!
I took it to the Apple store after work this evening and explained that I thought the haptic motor was faulty. The specialist tried it and he said he could feel a difference between the middle and extreme right settings, although he agreed the difference was not great.
I noticed he was wearing a Space Gray Sport the same as mine - lol so I asked him to compare the two, and I asked if I could see how the haptic felt on his watch. There was definitely a difference on his, and he agreed - but he then said that he didn't think they had any more in stock.
So I said "Errrm - I actually reserved one earlier today just in case!"
Boom! Replacement Apple Watch. I made sure to open and try it there and then and, yes, the haptic feedback on the new Watch was much better than my original one.
The fella is now a happy bunny