vireya, if you have any special requests regarding a specific diet that you require when you are onboard, you can inform Crystal ahead of time and they will try to accommodate you - gluten free, kosher, etc. If you have a regular item that you would like frequently and you are concerned that it will not be offered, meet with the maitre'd when you board or after, and Crystal will try to ensure that your request is met.
The Serenity has many dining options depending upon your flexibility and tastes (including Tastes). You would not have to pack a tie to sail Crystal, but I would suggest packing a jacket for man. You do not have to wear suits and a jacket will do as the jacket could match different pants, a tie is optional, and a tuxedo is not necessary except for those who choose to wear formal wear.
I cannot wait to be back on Crystal. The cabins are smaller. There is less flexibility in dining and one must follow more of a schedule. That being said, the onboard experience is excellent. The dining was fabulous, but because of my palate some dishes were more enjoyable than others.
On my first Crystal cruise, although I enjoyed the experience, it was difficult not to compare it to what I was used to after sailing on Regent almost exclusively for years. I had also sailed on Seabourn and Seabourn is much more like Regent. However, on my second Crystal cruise, I was much more comfortable with the Crystal "way". When you sail with them and accept the differences such as cabin size and less flexible dining times, it is an absolutely fabulous experience!