Although I take many of the comments in these reviews with a grain of salt I suggest you do the same with mine as many comments are subjective to one's likes and dislikes.
Having mostly sailed with Celebrity I have been spoiled by a superior line.
I found the Diamond Princess to be a little dated starting with the cabin. It needed some upgrades.
Embarkation was very good as well as leaving the ship.
I found the lounge entertainment to be very good and lots of good music.
The shore excursions were handled as well as can be expected.
I didn't care for the fact that we had to dock at so many container terminals and a long bus ride to the major cities. Maybe a smaller ship for me the next time.
The Horizon Court was upsetting and as Ray pointed out some groups would use it to set up their Ma Jong games while others were looking for places to sit. The food service area was terrible being one of the smallest areas I've ever seen. On top of that we had an outbreak of influenza on the ship and everyone was handling the same spoons in the service line. On Celebrity they have people serving you the food which is far more sanitary.
The staff on board were very good. Our room Stewart Leo was very attentive. We had any time dining and the waiters were excellent. The food was pretty good for the most part.
On the last night we had dinner in the Sterling Steak house and it was worth the extra $20.00.
Overall a pretty good cruise but I must say I will be going back to Celebrity for the next one.