My copy arrived last night. I got a friend to try out single card play with me, and it was hilariously bad. The gameplay is fine. It's Worms at its wormiest. The net code, however, caused us to see entirely different things from each other. Well, the first game didn't have that problem, but his system (the one with no card) locked up just as I delivered the finishing blow. My system moved on to the next round, and didn't stop the game until he reset. The second match went fine until I watched him walk a worm just a hair too far and tumble into the water. I laughed at him for a moment before realizing he hadn't finished his turn. He ended up in the drink anyway, although on his system he took one of my worms with him and reshaped the landscape a little. Fortunately, it didn't interfere with my next turn, which didn't involve any of those worms. If I hadn't won the game on that turn, however, very weird things might have happened when I got control of the worm he had killed or the one standing nearby. Unfortunately, there's no hotseat play, so we gave up on it and played Smash Bros.
I don't know if multicard play is any better, but I hope it is. I especially hope these problems don't happen on WiFi Connection matches, though I don't know how anyone could verify that. I guess if someone appears to do something really stupid, you can assume it's just the game getting out of sync.