I was in your boat a month ago or so. I played for a while but have quit again. (I played, by a factor of 10, far too many games on Isotropic.) The problem with Goko for me is that I found I was playing many fewer games per hour than on isotropic. This is due to several factors:
1. Lobby wait time is longer, due to problems both with policy and with implementation
2. On average, in-game mechanics are slower
3. Some things take longer to load than they are supposed to
You can solve problem 1 by paying, to some extent, because if you have all the cards, you can start a game, and (with extension) guarantee a good player will play with you. (Without extension you have to manually boot the riffraff). To me this feels like rewarding them for having an unintuitive lobby system -- on the other hand, they're a business and they have to find some way to get you to pay.
I'm not sure 2 is as much of a problem -- in fact, for a few types of games (scrying pool comes to mind), when 3 isn't happening, Goko is faster than Iso was, basically because if you are megaturning, it organizes your huge hand in a way that makes it easier to play quickly.
I think a lot of people would rebut my argument by saying that it's quality and not quantity that counts, and, if it were only for point 2, I would still disagree, but only on a personal level -- that argument makes sense, but I still prefer Iso's speed. Because of points 1 and 3 though, I think it's more than a personal preference and is something Goko should strive to fix.
Other than speed, I think Goko is fine. Personally I am an internet minimalist -- I used text and not picture mode on iso -- and so I think I'd prefer iso's look and feel even if Goko were the exact same speed.
Tl;dr goko is ok but too slow