First let me say, we have been on both Oasis and Allure, both times January (2010 & 2011). Weather was great on both. The ships are very large but once you find your way around, easy to maneuver. The direction boards at the elevators are a big help, especially looking for restaurants. We were with another couple who was not on the Oasis or the Allure before so it was nice being able to guide them around.
I have read almost all the "negative" reviews about both ships and cannot truly agree with any of them. The cabins were clean, the cabin service was wonderful and they were extremely polite. Plenty of room for clothes and storage of suitcases and such. Only thing was the refrigerator never got that cold so we had to add ice to drinks.
The restaurants were what Royal Caribbean is - Windjammer crowded and food a typical buffet but good. We only ate there once on each ship. Breakfast and lunch in the dining rooms was very good, we loved the Cafe on Central Park, their RB sandwiches are to die for. The Hot Dogs on the Boardwalk were really good - that with a milkshake from Johnny Rockets brought us back to NY. The main dining room food was as it is on all RC ships - good but not fantastic. BUT, I didn't have to cook it and it was served with a smile. I love their "savory bites" and they made sure I had plenty of them at dinner. Too bad I couldn't take any home. My favorite place to go during the day and after the casino (1:00 am) is the Promenade Cafe - sandwiches are really good. Their coffee there is also good and they are open 24/7. My only complaint is the coffee in the restaurants - really strong and sometimes tastes burned.
While we were there they were filming a commercial for RC (Internet only) and stars like James Brolin, Jenny McCarthy, Dean Cain and Scott Elrod were always wandering around the ship, filming clips here and there. It was really fun to watch and, although they were blocking off areas for their filming, it was never an inconvenience.
The shows were as expected - we reserved each of them before we boarded. If you go into RC's web page where you do online booking, there is a tab to guide you to reserving the shows. It opens up about 90 days before sailing so you can get it done before going on board.
The smoking/non smoking casinos are really great - although the machines in the smoking area are better than those on the other side. Sometimes too crowded in either one.
Overall, I would rate both ships an "A". Would I go back on them, probably not. The experience was something all cruisers should try. I still like the smaller ships (Freedom class and lower) because they are more intimate. Our very first cruise was on the Sovereign of the Seas and that is a midget compared to this. I still like that size ship. We are going on the Jewel of the Seas in October for a repositioning cruise for 14 days. Looking forward to that one. Whatever you do - enjoy the ships - they are magnificent.