Very good. Great even.
But there is a problem. Whatsapp has already won the chat/calls app war. Watch it grow massivly in the next year, i promise.
Mostly due to incompetence of MS and Google.
Frequently i get kicked off of Whatsapp because my phone has been idle for too long. Frequently my messages are out of order between the web client and the android client. Semi-frequently Whatsapp hangs when sending messages, sometimes dropping them (i assume due to my phone going idle).
I wouldn't recommend anyone to Whatsapp.. for UX, at least.
However, WhatsApp is already at 1bn users [0][1]. Expanding from that is going to be very hard.
0 - http://www.theverge.com/2016/2/1/10889534/whats-app-1-billio...
1 - https://en.wikipedia.org/wiki/List_of_virtual_communities_wi...
Globaly - maybe, for now. in some countries, however, it's not as popular as Telegram or Viber, for instance. (like Iran, for example)