My take, and everybody is going to be different, is that DCL is worth the extra cost if you are traveling with small children. DCL truly excels in this area, and the extra cost is well worth it.
When traveling with just adults, I will take Celebrity over DCL for my money. The crew is just as accommodating, I found many more activities geared to my tasted on Celebrity. Celebrity has an adults only area that is actively enforced. They have an awesome "no saving lounge chairs" policy. Sure, all ships claim it. On Celebrity the towel/pool stewards actively remove items people are using to save chairs if nobody show up to the chair for an extended period of time.
I found the food on Celebrity to be just as good, if not better, than on DCL
I will say that the shows on DCL, as a whole, are better. Every night on DCL is a stunning show (but you do get repeats on a long cruise). Celebrity has some stunning shows as well, but then every so often they throw in an act that is just OK. However, on Celebrity every night is a different show. So you take your pick DCL with 3 awesome shows that keep rotating, or Celebrity with 7 different shows, with 2 of them being passable.
If pricing was the same, I would call it a toss up. But with DCLs inflated pricing, It's not a product I am going to pursue for adults only crusing.
My experience with Celebrity was horrible. The ship was well past it's dry dock time. There was rust all over the place, including the hand rails by the pool. The rooms where TINY. We do not have a large house but my master bathroom is bigger then the room on the Celebrity ship. The staff was very rude and just had the attitude that they did not give a crap. You would hear people talking about it saying how these things would never happen on a Disney cruise. People were just lined up at guest services to complain about how bad the staff was. The food was OK, but the dinner in the main dining room was definitely not up to the standards that DCL has. There is no way you were getting a filet or lobster at the MDR. I felt like everything was an extra charge and that the tables that they set out in the hallways made it feel like I was in a cheap flea market. They allowed smoking in some of the inside rooms that were hard to avoid crossing the ship plus you could smoke anywhere on an open deck, including by the pool. That was a big issue for me because of my allergy to it. I don't like how you have to go up to a bar(which allows smoking) just to get a soda. When it comes down to it, you get what you pay for.