I did a 7 day western Med cruise - roundtrip Barcelona on RCCL Liberty of the seas. I’ve probably done 20 cruises (Caribbean, Bermuda, Alaska) and this was by far my favorite one.
We got a balcony cabin, and I wish I hadn’t spent the money on that. It was a very port intensive cruise with only one sea day, so we really didn’t have a chance to use the balcony.
Our route was Barcelona, Toulon (Provence), Villefranche, Rome, La Spezia (close to Cinque Terra), and Nice. Each port was spectacular.
A few tips:
Fly over at least one day early. Stay at least an extra day at the end. You’ll have extra time to relax and adjust to the time difference.
Book private excursions. They are cheaper and can usually be customized to your needs. On Cruise Critic, join the roll call for your cruise. Lots of times people will be looking for extra people to fill out the empty spaces. Cruise Critic also has a lot of good info on the European ports.
I wish we had booked a cruise that was a little longer and had a few more sea days. We did private tours that usually started around 8 am and didn’t get us back until an hour or so before all aboard. By the last day, which was a sea day, we were whipped. I really could have used another sea day or two in the middle of the cruise.
Unless you really like hot, humid weather and big crowds, I would try to go in late spring or early fall. We went the first week of September, and it was still very hot.