This past week I have been heading over to Goko more often than Iso - primarily for access to DA cards. As previous people have said, the experience is reaching a point where I might shell out the dough for cards. I have to agree that it lacks the same kind of competitive feel as Isotropic. But if they continue to take player requests into account, and the player base continues to grow as it currently is, it may get there.
+'s
Card art
Dark Ages
Relatively quick gameplay if your opponent knows what they are doing
Relatively short wait for a game if you find an opponent who you enjoy playing with and agree to matches
Player base that is growing in competitiveness
It is completely free and I am finding that many people I play with own all the sets
-'s
Lack of automatch means considerable wait times in situations other than what I mentioned above
Lack of any sort of misclick protection - major annoyance as you get used to the interface
Lack of a log that is actually usable during gameplay (w/o opening the log screen)
Lack of a single room - I general bounce between the occupied rooms to find games
Issues with dropped players/disconnects
Occasional bugs
The revamped store with a megapack that costs more than the individual sets combined
Regarding the IP debate. Most boardgame companies require payment for access to the online equivalent. Hasbro has most of their games out through Pogo.com - which costs $5 a month. Settlers of Catan also cost $5 a month for access to all expansions etc. At the end of the day, one can go onto Goko and play base for free, with a high probability of playing all sets for free (because someone else paid). I know money doesn't grow on trees, but $45 isn't that much to ask for access to an online player base of dominion players w/ the chance to play cards from all sets. THAT is the privilege you are paying the $$$ for, and it is something that was not promised to you when you bought the physical sets. Heck, I've had hangovers that cost me well over twice that.
Lastly, I think its clear that Goko is marketed towards people who prefer to play Dominion online. People like the top 10 on Isotropic who have logged an average of 5500 games per player (and I'm guessing tat and dekomri are alts, which would inflate that number). That's less than a penny a game if they were playing on Goko.
But if you don't want to pay...don't.