For the most part, city riding is pretty well served by Google maps IMO. A few years ago, following Google maps cycling directions me and a couple of friends on road bikes were led through muddy forest trails, old rail road tracks and green lanes on a London -> Paris The difficulty with cycling directions is that there's not a 1 size fits all solution, a roadie needs smooth road but would prefer it quiet and scenic,…
With my site, cycle.travel, I've taken the opposite tack: generating quiet, safe routes for leisure and touring rides, while still being as fast to generate routes as Google Maps. Sure, I want it to be usable in cities but it's not the main focus.
People have used it successfully to plan month-long tours across Europe and the US. One of my favourite bits of feedback was https://www.cyclechat.net/threads/swindon-to-orkney-a-wet-we... , where someone just punched in a start and end point at opposite ends of the UK, and rode the route it suggested without any tweaking.
https://cycle.travel/map if you want to play - always happy to hear suggestions/feedback (and thanks to Jake for including it in the post!). Currently Europe/North America/Australia/NZ only.