Having sail both HAL and Celebrity (multiple times) there is a difference and it's not just passenger AGE.
We sailed a 10 day on the Oosterdam. The ship was beautiful and spotless on our sailing.
Service was above expected in every department.
Our cabin suite was larger than any of the suites we've had on Celebrity (not including of course the Penthouse)
The gym and spa area are exceptional, having current equipment and again spotlessly clean.
Passenger age range varied, but most over the age of 40+...there's lots to do on board ship...BUT events, shops, etc. do close down early! We found most closing up by 10pm.
There's a different movie in the Theatre every night, lots of available TV channels (if you're into that) we had a DVD player in our room with 11 pages of movie choices.
Food is subjective, having said that, we found the meals varied and excellent.
HAL is rated on the upper end of Premium and passengers sailing on HAL appreciate and expect quality of service.
On our recent 12 nights cruise on the Celebrity Infinity...
The ship was in good shape, but not as clean as before. Windows throughout the ship were very dirty and hard to see through. A vital issue since we were cruising Alaska.
Our suite was nice but on the small size...
General service excellent of course. No complaints at all.
Entertainment good to excellent.
Food...Celebrity does have good food!!!!
We did NOT have a DVD player or VHS player in our suite
Will we sail Celebrity again...most likely...
Will we sail Holland America.... Absolutely!