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 <24hr attempt (we took 26hrs).
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, a mountain biker would rather those trails we found and a commuter/hybrid would be fine on those in short bursts but probably prefer the speeds of the roads.
If I'm doing something of an "epic" route these days I'll spend a bit of time trying to find a suitable GPX that I can sync to my watch for directions - usually that'll come from Movescount, OS maps, Garmin or just someone's blog of a route. For most other things, Google maps works fine.