I have never read a Mills and Boon,so I can't judge them.I know several women who do read them and enjoy them. I like a good murder mystery,light on violence and heavy on mystery.I am keen on sci/fi/fantasy books,but not ones about vampires or zombies. I like adventure and derring-do. In sci/fi, you can have anything you want,monsters,heroes,people with magic powers and so many other variables that there is an endless supply of creative ideas.
One of my favourite - most read - writers is Charles Hamilton, who wrote under maybe 50 pen-names, the most famous of which was Frank Richards: 50 words a minute, six hours a day - 18,000 words. He kept two or three text-based comics (maybe 40,000 words or more an issue) going for more than 30 years, pretty much single-handedly.
To be fair, a lot of those words were "Ha, ha, ha!"