Was about to post it. :) Registered.

I had to stop watching EURO for a bit to register too! =)

What is it some online only MMO opr something. All I saw was signup, client etc.

No, it's not online only though it does have competitive PvP mode and crossplay with XBOne. There will be a fully featured single player adventure and player vs AI mode too. You can read more here.

Fun fact: Went to register as soon as the conference announcement came, entered the info, clicked register, got greeted by Theodore holding the globe with the "We are currently overwhelmed by our popularity" message.

Wow, guess I was the earlier ones.

Considering that Gwent offers in app purchases, I doubt it will be coming here.

They announcecd it at E3 Micosoft, so I think Microsoft wanted it to be first there.

Try two almost immediately worked though, so most likely a lucky (or unlucky) coincidence.

What the heck is GWENT?

An ingame card game in Witcher 3. Similar to what Arcomage was in Might and Magic 7 (or was that 8?).

Ah, nevermind then.

Just a F2P card game with in-game purchases. You can play online or off. Internet connection is only required to download the single player campaign and purchase items if you don't want to play the competitive mode.
It's free and there's a single player adventure mode, so I don't see any downsides to trying it out.