Citymapper's UX is really awesome, and I always use it as my example of the degree to which attention to detail is so absolutely vital in this sort of app. Like, first-class, best-app-I've-ever-used level of UX.
I'm still not totally sold on their routing algorithm in London, but I'm not sure exactly what's wrong with it - all I know is it often suggests routes that no same person would take. It definitely seemed to get a little worse maybe 6 months or so ago; it's possible it's just been tuned in a way that doesn't get on with my usage pattern.
I find that it's become a bit worse as I've become more familiar with London. For someone who doesn't know the city at all it's perfect, but once you know the tube map and various local details, some of the options do seem a little odd.
One of the devs posted in this thread that they favour routes with more frequent services, as people often don't want to travel immediately. I'm not entirely sure I agree with this thinking in a mobile app, but it could explain some of the less optimal routes.
Yeah, it doesn't really get all the tiny things that you have to know the system to know. For example, on trips where multiple lines travel on the same tracks, the average wait calculation looks to use only one line's frequency (Liv St to Edgware Rd, "5 min avg"). Time to change between lines at interchange stations also feels unrealistic (1 minute Northern-Bank to Victoria at Euston and 2 minutes Victoria to Piccadilly at Green Park?).
I'm still not totally sold on their routing algorithm in London, but I'm not sure exactly what's wrong with it - all I know is it often suggests routes that no same person would take. It definitely seemed to get a little worse maybe 6 months or so ago; it's possible it's just been tuned in a way that doesn't get on with my usage pattern.