Great question - but there's nothing to be afraid of!
Thre are certainly differences between RCCL and Princess, but they're more issues of overall style, activity levels and dining preferences. If you're happy with the Explorer of the Seas, you will most likely be pleased with Princess as well. You might even find that Princess gives you a little more value than RCCL (imho), but then again, if you can't imagine sailing without a rock wall and ice skating rink, well, the RCCL Voyager class is definitely for you.
You already know what RCCL has to offer, so here are some of the Princess features that you may not be aware of (depending on the ship, of course!):
Personal Choice Dining, which gives you two dining options - Traditional Seating, which, like RCCL, features a large dining room with assigned tables and set dining times, or Anytime Dining, which gives you the flexibility to eat when you want and with whom you want anytime from 5:30-10:00 PM, either by simply showing up at the dining room (just like a shore-based restaurant) or by making a reservation if you wish. But please note, they generally will not take dining reservations for 6:00-7:45pm; it's simply first-come, first served. Whichever you choose, you will get the same menu in all dining rooms, with the exception of the Diamond and Sapphire, which have four themed dining rooms for their Anytime Dining guests featuring specialty (Southwestern, Asian, Sterling Steakhouse or Italian) menus as well as the main dining room menu. Traditional Dining guests on the Diamond and Sapphire also receive selected specialty menus as well as the regular menu. Breakfast and lunch in the dining rooms are all open seating, and the Horizon Court buffet (quite good and featuring dining room menu items at dinner!) is open 24/7.
You'll also find Movies Under The Stars on Caribbean and Grand Princess (other ships soon!), which transforms the pool deck into a giant outdoor theatre, complete with lounge chairs, blankets and free popcorn!
There's plenty to do on Princess; everything from breakfast, daily trivia contests (my personal favorite - watch out, Ken Jennings!) to lunch, pool games, full-service spa and gym, snacks, first-run movies, dinner, lavish production shows, more snacks, a full casino (player-friendly blackjack rules, but the video poker pay tables aren't so hot) and a late-night meal in the Bistro!
I've found the service on Princess to be first-rate, the cabins spacious and well-appointed, and the food is teriffic!
Let me know what it is you like best and least about RCCL, and I'll do my best to give you an honest comparison! But I can't believe that you wouldn't just love a Princess cruise.
All this talk - I'm ready to go now!
Star Princess '02/'03/Sept'05
Diamond Princess '04 (twice!)
Island Princess '03
Sun Princess '02
Celebrity Infinity '02
Golden Princess '01
Sea Princess '00
Norwegian Sky '00