I think a lot of it is in your expectations. I have only been on one NCL ship, and that was a while ago (and it wasn't the Sky) so I can't respond specifically. When I was on NCL I liked some of the food a lot, and some of it I was disappointed in - but that was due to my own personal preferences. Remember that many - possibly most- reviews are written by people with an ax to grind, so you are likely to get more negative remarks than positive.
If you have never cruised on one of the luxury lines and are not used to 5-star gourmet food in the finest restaurants, you will probably find most of it to be good, and some of it to be very good or even excellent. Don't worry about it - relax, enjoy and have a great time!