As I posted in another thread why some members can and some cannot see various buttons/functions etc is way beyond me. All I can do is tell you my experience so far.
On Monday when GH switched over I couldn't see any of them, then by Tuesday morning some of them, not all though, were there then later I had more functionality. e.g when the "like" button appeared that was all it did - it added a "like" and it was a few hours later that the smilies bar appeared for me.
And I see there are other additions this morning - yesterday there was no info. below our Avatars but I see it now details Date Joined; Messages (a.k.a number of posts) and Points (which I presume is some kind of reputation?) and the number of replies and "view count" is back on the threads.
How long will it take to complete the switch? - I have no idea
What will the new GH look like when the build/migration is complete and the glitches ironed out? - I have no idea.
Will I like it? - I have no idea, lets wait-and-see.
What was my 1st thought when I heard we were switching to a new platform - "Oh crap, I like what I'm used to and don't fancy having to get used to something new.... will it be easier to use or will some things be a pain... will I loose my old posts... will I loose my "thanks" total etc etc"
But I take W!nston's point that the old GH had been running on the Vbulletin platform since 2008 and after such a long time it was I guess inevitable that there would need to be a major update at some time.