For me it's the frustration that you can't see messages of encouragement any more - text far too small. Also you can't see how many other riders are in the race, or how many spectators there are. Oh, and you have to hit the up arrow to see the ave. watts, speed etc on screen which is far more important than the standard view.I don't enter my password, I just get logged in? There was a issue when this first launched with passwords needing to be reset. Since then I get put straight in bsim's main page. I still suffer from bsim crashes though. But I think it is most likely the nuc drivers at fault, I can't seem to get them to update.
Yes the interface, although prettier, is not as user friendly. The limitations on numbers of sessions displayed for each catagory can be frustrating.
I do like the extra info re: how long each gradient section is - this is really useful and helps to gauge whether attack a 9% (say) as it's only 100 mtrs with a 4% rest next, or if the 9% is 300mtrs.