We went on a Norwegian European cruise in the fall of 2014 and were more than pleased (see review). Celebrity is supposed to be a step above, and we found this wasn't the case. Be prepared for a long list! Remember, we had a great cruise on Norwegian 4 months before, so I'm not just a negative reviewer:).
1. Check in was confusing and long. We booked Aqua class and booked our kids in two rooms in Concierge. They wouldn't let us go together and ushered us through the line to a special check in. Once there, we watched for 30 minutes while they brought people from regular boarding over into our area and checked them in. Our kids were in a long line and got checked in way before us. Confusing and exhausting.
2. We found it nearly impossible to reach guest services via phone throughout the cruise. When we asked about dinner reservations, we were told we had to go the restaurant and talk to them directly, but could only do it at very limited times as they couldn't do reservations during dinner hour as they were too busy.