I was quite surprised by how much I liked the Oasis. Frankly I couldn't care less about the ports with that ship. It is all about the ship as the destination. But, I will say that unless the price drops RCI will indeed have problems filling both the Oasis and the Allure every weekend (one leaves on Saturday, the other on Sunday). I'll return to one of these ships but I can't see anyone making a habit out of it. Once or twice will suffice. On the other hand, I will easily return time after time to one of RCI's smaller ships.
The Grand Class are nice ships, and the variations on the original design are good. Having a magrodome pool is something that they all need. RCI missed the boat on that with the Voyager and Freedom classes.
I keep thinking back to the great cruises we've had over the past two years on ships which are 12 to 25 years old and carried ~2000 passengers or less. As I often say, the success of the cruise is really about the crew and the passengers attitude, and not so much about the gizmos on the ship.