We flew WOW in September to Frankfurt. It was a few hundred dollars cheaper per person than the other carriers, but of course there were fees for extra luggage (we didn't take any extras) and food was was an additional charge.
It was a little hectic connecting in Iceland, because all WOW flights from the US arrived around the same time, and we had to dash through customs along with a few hundred other people, thence to our departing continental flights. It wasn't too bad, overall. Glad they waited until now (not last September) to go out of business.