The new interface looks childish and is unusable in landscape mode. The next instruction box at the top is too big. The notifications are horribly big, and the ones that show when you stop at a traffic light are worse, with the black background.
The map looks drawn by a 4 years old in crayon, seems to lack a lot of the information it had on v3.x., the map lines are too wide.
Having functions that only show when you tap the screen is very bad in usability terms.
To top all that, the interface is so heavy that it now takes three times as much to start and hangs frequently while I am driving, staying unresponsive for tens of seconds - and that is not a good idea for a GPS driving app.