I booked my flight to Paris for September on Wow Air (Baltimore to Paris, round trip through Keflavik). It's a few hours longer than a direct flight but not really longer than any other flight with a connection (10+ hours there, 11+ hours back). The booking price is great, $500. Cheaper than any other option.
Like most low-cost airlines, however, you have to make sure the other costs work for you. My other costs so far: a seat reservation for the flight leg into Paris for $9. I like to hit the ground running so I paid for a seat on this leg. On the others, I'm still deciding whether I care enough to purchase a seat reservation.
The downer cost right now is for a carry-on bag. You get a whopping 5kg carry on for free. To bump the carry on up to 12 k costs 16 euro, but that's for each leg. So a normal carry-on bag costs a little under $50 each way (two legs). For a 20 kg checked bag (plus your 5kg carry-on) the cost is $68 each way (two legs). I'm sure I'll carry-on over to Europe. It helps me get out of the airport and on my way quickly. Assuming I do a carry-on for my whole trip, the cost (with one seat reservation) is just over $600. If I check on the way home, add another $19.
The next best flight prices I found are around $680 (then up quickly from there). With those I'd probably get free carry-on but likely also pay for a seat reservation on the lowest cost options.
Ultimately, I'll save some money with Wow Air but not as much as one might think on first blush. Am I disappointed? Not at all, but I might be depending on how the flight goes. Most airlines are like cattle cars now anyway, so if they get me there and back on time and in one piece, I'll be happy.
I'll report back when I get back in October.