I am an isotropic refugee who tried Goku for the first time yesterday. I tried to approach it with an open mind because it's human nature to want to avoid change, and isotropic has set a very high standard.
The good news is that the interface is polished and reflects the home game well. The graphics are beautiful and the layout pretty straightforward. I didn't experience any crashes and although there were times I suspected bugs (eg, I could swear it let me trash > 4 cards with Chapel), it may very well have been user error. Coding a clean UI is not easy no matter how many webkits there are available these days and I think the team here did a good job.
The bad news is that there are some very fundamental things missing here and, in my opinion, this is not ready for primetime until they are addressed. The most glaring problem to me is the lack of a middle ground in the UI, where one can see what's going on in the game without having to be bombarded with animations (which I'm quite certain any users who play this for any reasonable length of time are going to want to disable). The animations annoyed me after about two games so I turned my settings to "very fast" to disable them. But in this mode, the game is basically unplayable because it requires consulting the log every turn to figure out what you or your opponent did. Things like crossroad reveals and jester attacks are very cumbersome with the animations disabled (and, in fact, even in "fast" mode they don't provide enough time for old fogies like myself). I was playing one game and ended up buying three curses because I thought that they were the copper targets for my swindler. I have no idea how this managed to pass testing. Fortunately, the solution is very simple. There is plenty of space underneath the cards, and there needs to be an option (which I'd default to "on") to display text there, similar to what is written to the log. So when something is swindled, it can say "You swindled a copper..." and so forth.
The other major problem is the matching setup. First off, separating players into rooms is completely unintuitive and awkward. There is no real technical reason why the lobby can't support a huge amount of players (even if the games get hosted on different machines on the backend). Furthermore, there is no logical filtering of the games in play. I don't care about games that are in progress (which is 99% of the games at any one moment). I just want to see what's available. Ideally I could say "show me 'pro' games". More ideally, "show me 'pro' games with dark ages sets". Even more ideally "just automatch me into a 'pro' game with a dark age set". Is there any reason why everything is done manually here? All I'm doing is bouncing from room to room in search of that elusive 'pro' game that might appear, and most of the time I'm switching too late, just as if I were changing lanes in traffic only to see my original lane speed up.
Overall, I think this thing is close, but at the same time these very fundamental concepts need to be addressed before I'll be buying in. And I suspect others feel the same. And I'm hardly a "hard core" player-- this is just common sense stuff. While staying true to the board game is great, one of the advantages of a computer version is to improve on those parts that are more readily accessible (the lack of shuffling being the obvious one, but other things like text feedback of events rather than having to squint at small cards). Isotropic was an example of a system that did this in a very minimalist fashion. There's no reason Goku can't do the same while still keeping their impressive glitz factor.