Joey, we have done 8 Princess cruises and one major difference (which has been discussed here already) is the balconies on the Sun class ships. All other classes, Grand or Diamond class have wonderful balconies all glass and vary in size depending upon category or where it is situated on the ship. BUT in the Sun class all the balconies (other than the Grand Suite) are inside the superstructure - and look like they've been carved out. The problem - when you sit on your small balcony you can't see the sea, because the sides are steel. We always travel in Mini-suites on Princess, but truly on this class ship an outside cabin is just as good. Now that is our personal opinion only!!!
The anytime as opposed to traditional dining. Yes they can seat just two people, you can also book traditional now and then say on your 2nd night onboard give anytime a try at the time of your preference - and compare for yourself. When we get a good waiter we just book his table for the rest of the cruise.... but go to the restaurant at a time that suits us. Anytime dining on the Sun class also never has a wait time for a table, sometimes on the bigger ships you may be given one of those "flashing/vibrating" thingees and go to the bar for a drink to wait for your table to become available... this doesn't happen on port evenings, but sometimes on days at sea.