Well, i started to learn ZBrushCore when it came out last year and a couple of weeks ago i upgraded to ZBrush. So learning ZBrush is therefore easier for me. I read also many times in the past that some people find ZBrush's UI alien. I personally like the UI very much but must admit that i'm still a beginner and have to learn more about all the amazing tools ZBrush provides.

Regards
Stefan