EV 12 is the North Sea route.
I've ridden several sections of 13. In some places it's very easy to lose the route, the signage can be patchy. Germany and I guess NL is probably better than average. Also the route tends to wander around randomly like a sustrans path often for no good reason. Surfaces can be variable, but in this respect not as bad as some sustrans can be, fine on 25/28mm touring tyres.
(OT) I've just had a look at EV2. From Warsaw it goes *almost* to Brest (not that one, the one in Belarus), then realises you can't cross the border there with a bike and doubles back to follow the border to somewhere you can. It's the mistake I made last year, but you'd think someone putting together an international bike route might have a bit more information! (Actually, I didn't do the double back bit, I put my bike on the shuttle train.)