Fair enough. There is a certain romance to crossing the atlantic by ship, though. That's been on my bucket list for a while - IIRC a ticket is on the order of $1-2k for a weeklong journey from UK to US.
The round trip idea is unlikely to work well unless you're willing to wait awhile as the cruise ships are repositioning to handle specific seasons (e.g. Northern Europe in the summer, the Caribbean in the winter).
The exception is the Queen Mary II, which is an ocean liner that still does regular trans-Atlantics.
If you can afford 2 weeks off for a round trip, you should really take at least a week in the country to arrive at to see it. Cruises are nice, but you don't see the culture of the places you go. Either fly back, or take more than a two weeks. I recommend fly back, the one way trip is a once in a lifetime thing, but the return trip seems like it would be repetitive (having taken several cruises, though none trans ocean)
Of course both Europe and North America are large continents with a lot more to see than you can do in a week, but few of us have the budget to be a world traveler for a few decades to see everything.
Right, the point is it might be six months, since a lot of cruise lines will do only one crossing for northern/southern hemisphere summer toggling.
e.g. here in Seattle the cruise ships that go between here and Alaska make a single trip down to Australia or somewhere in the fall, and then don't come back for half a year.
Ah okay, I guess I was thinking that OP was talking about a more traditional sailing ship or something rather than a cruise ship! I've lived in Europe a few times and really enjoyed it but going across the Atlantic by boat is on the bucket list