First, I'll state that my experiences were my own, and perhaps I just didn't "Go to the right places" or "do the right things", but we stayed in the following cities for 3 days/nights on average, and slept very little.

I wasn't a huge fan of London. It was awesome to see of course, and be there, and see all of the things from movies and history. But it was expensive, busy, people weren't friendly, and other than seeing the sites and museums it was definitely a place I wouldn't want to go back to anytime soon.

I was also not a huge fan of Berlin. Kind of bland, boring, and quiet. The people weren't unfriendly, but the entire town had this like "seriousness" to it that I just didn't enjoy. They were unfriendly, dry, and stern at every place we went to. When we were there, we are very much "off the beaten path" type people. We would meet up with locals, go to local bars and restaurants, and try to stay off the tourist path outside of the museums and main attractions. Just didn't have a good time there. I had the exact opposite experience in Munich though.

Didn't really dig Barcelona either. It's beautiful, and on the med, and there are some unique things to see there, but overall it wasn't that exciting. Though, we were there during their time of year where they all apparently go on vacation and shut up shop for two weeks. Most of the stores and restaurants were all closed. It was so weird, it was a ghost town except for some of the more nightlife/bar related areas. I could barely find a place to buy a pack of smokes. So perhaps it would deserve another chance some day.

Also, Paris, despite every teenage girls dreams of it being this super romantic and beautiful city, I found it dirty, too busy for my tastes, and kind of disappointing. Sure, the museums are great, seeing the sites are great and like living a movie, but as a city and culture I found it just kind of "meh" overall. But the Normandy country side, and the riveria were awesome and beautiful cities, just not Paris.