Rooms: Oasis does have a variety of suite offerrings including multistory suites etc. However, for our room which was a standard room for 4 (maybe five) people with pulldown and pullout couch, Fantasy wins out. Size of room, Disney's are largest at sea. Storage space - Oasis was very cramped as far as place to put clothes for 4 people (we still have not learned out to pack efficiently!!).
The two bathroom layout for Disney is flat out better. The sink area, bathroom storage, counter layout is also a big plus. Also, we really missed Disney rooms ability to pull privacy divider curtain. Helps for when it is time for us to tell the kids to go to sleep, or getting up in the morning to go to the gym without waking everyone in room. hower in DCL and Fantasy's shower also much much roomier (with a tub for those of you with little ones that like baths). That said, Oasis' tubular design contains the spray well (pet peave of DH is water on bathroom floor).
Kids club: Hand down, Fantasy wins out. Our 10 YO wanted to go to the club every day on Fantasy. When we took the tour on Oasis, the rooms appeared small and uninteresting. There was some interesting science lab stuff, but where were the computers? Games? Fun things. Our 10YO therefore did not go to the clubs - there was no dining room pickup. This is possibly a problem for those with younger kids who rely heavily so since we did not have that age, we cannot comment on how they are once the kids are there. We just know that the 10 did not find it appealing enough to want to even check it out.
We will have to say that with so many people on the ships, there is very high percentage that your children ages 10 and higher will meet others at the pools and make connections to spend their time.
Back to our original comments, there is almost a dichotomy of vacations: Do you want ones centered round the MDRs where you spend 6 nights, your kids are with you, they are picked up for kids club, this if for you. If you like the vacation where mom and dad wine and dine in a variety of venues, take in ship activities; while kids are running amok enjoying their activites, their own dining venues - with occasional reconnects, perhaps this is for you. Comment on this: In retrospect, there is a leap of faith you are taking on this. The (near) drownings give you something to think about. Also, at the end of the day, you are on a cruise ship with 6000 other people. You have faith in that their demographics are the same as you - vacationing families etc. In the end, it is something to think about.
One cool thing that Oasis has one-upped Disney in the photo department: For most part, no handing people your KTTW cards while you are getting your pictures taken. Disney might use facial recognition software to group your photos, but RCI's system really leverages this - no need to stop and give you your card - the photographers meander and take pictures at many venues - and you keep going with your activities. No time wasted looking through shelves of photos - your pictures are grouped together automatically - there is an occasional software mistake but this is a cool feature. (Gotta get this at home)
Finally costs: We said that before "extras" Oasis was upwards towards $6K while Fantasy was over $9K. Here is the catch: RCI will nickel and dime you to death. For example, basic water, lemonade, ice tea is free. Pop package is spendy and adds up. The specialty restaurants add up ($30 here and there or select alacart). Same thing with spa and fitness - a yoga or fitness class might cost $10 or $15. Some casual restaurants also cost. Also, it is our impression that equivalent offerrings for RCI are more expensive - similar spa offerrings or photo packages cost more but don't quote us.
On costs, we did purchase an alcohol package - for somewhere around $60 per person/day you could drink all you want tips included. This worked well for us and it was convenient to just hand the person the card at the pool and get it back without fumbling.
Crowds: With close to 6000 guests we never felt any more crowded than we were on the Magic or Fantasy. Also, like those ships, there was always a time and place for solitude.
Technology: The Oasis and Allure are technological wonders. Due to size, the ships barely rock so for those that don't want to sail for seasickness, these ships are for you. As a matter of fact, is bizaare as it seams, you almost want some turbulence and rocking to get that at-sea feeling.
In concluding for us, with teenage kids now, we think that RCI big ships (Oasis and Allure)is a likely progression. Why? Because it fits our needs. Because of variety and options for entertainment, food, excercise, sun, rest. We definately will return to the Fantasy (perhaps for family renuions, Christmas sailings etc) and we are already planning a return to the parks, but Oasis and Allure definately will get a slice of our cruise vacation budget for the time being.
Hope you guy liked the review (please remember this is opinion) and hopefuly this does not offend too many people to post on this board.
I went alone this year, kids will be coming next year. They both love DCL, but our group we'll be traveling with will provide all the activities they'll need/want on RCL. Though I'm working on making a mailbox-y type exchange like the FEs 
