I think the Spirit class is just about the right size.
All the amenities of the larger Carnival ships (except no fish n chips) with about 700 less people.
I have not sailed on the Oasis...but from the very first designs released...it looked like a huge mall to me. That is just the first impression I got.
And when my friends went on it (they had a wonderful time)...but their complaint was that you could see the Ocean AND it did not feel like you were on a ship. They always book an interior cabin. She said it did not feel crowded.
She also said she did not like the fact that she had to "schedule" the shows. (sadly one of the downsides to sailing with that many people)
She said she does not go on vacation to live by a "schedule".
And that the nickle and diming seemed worse to them than on Carnival, Princess or NCL.
Now having said all that, there are obviously enough cruisers who DO want that kind of experience.
It just isn't one that I want.