Slow burns are good if done well, and usually what most are looking for. After all if you want a quick burn you can just watch a video/movie. But for a slow burn to work you need good character building and a good gameplay loop. If either of these fail it usually results in a bad game or a...
For mobile gaming I like mo po ga a lot. For desktop it's this place if I have the time for it, and Nutaku just to kill a little time and play something idle-like.
I actually have no preference when it comes to engine. As long as there is actual gameplay (not just navigating through a story) use whatever engine works for you.
The first one ages and ages ago was a game called Wet: the sexy empire. But even before that it was leisure suit Larry (though i don't quite sees that as "lewd"). When the internet took off it turned to early flash games, sim brothel and the sorts. The nostalgia is real
I quite like Heroes Harem Guild. Not the best of graphics or animations, but somehow I got wrapped up in the story and premise. Hope an update comes out soon.
If the premise and story progression is good, then html games can be good. If it's just about showing you videos fast forwarded and you actually have some active gameplay, I quite like them, at least they are engaging.
Last game I recently tried that had a good premise was Just One More Chance...
Games that requires a bit of buildup, active play (quests, tasks, stats etc) and has a nice story to get attached to.
Somehow Heroes Harem Guild hit most of these for me. Been a while since it's updated but I think the dev is still active.