I wear a black velvet fancy pant suit for formal occasions - no problem ... and lots of the men wear dark suits rather than the tuxes.
I'd recommend taking a taxi to the ship - saves waiting around for a bus to fill up.
Had concierge class on the New Year's 5 night cruise ... not much to write home about, BUT did get flowers on the desk (changed once), a beautiful rose in the bathroom (died and never replaced), leather holders for your sail and sign card, at the very end of the cruise got a purse thing that turned into a shopping bag (would have been much more helpful at the beginning of the cruise). Never saw a pillow menu - but had already asked the steward for the goose down pillows (recommended by a friend who had had CC before), fancier robes, better breakfast menu (actually better than the penthouse suite) - but in either case, you can write in what you want. With CC, you also get a free bottle of champagne and a bowl of fresh fruit the first day ... and 6 canapes every night (2 are caviar).
Would not pay the extra again. Was supposed to get priority boarding and got there at noon - very officious man made everyone get in the same waiting line (said I should have been there earlier - when they recommend not getting there until 2 PM).
Food in the dining room was only so-so - but Murano's was outstanding - do try it!
Celebrity is more expensive drink-wise than my favorite line (Princess) so I suspect I will not sail with them again.
Because we were with a very large group (146) of CruiseMates, we got a lot of nice extras not normally given to cruisers.
This is just my opinion and by no means that you won't have a great time - you will because you'll be cruising. What could be better.