Very difficult to compare Regent with anyone other than Silver Seas, and Seabourn, and that
is also tough to do. Every other cruise line operate differently.
Regent is all inclusive. The price shows all inclusive, but does allow you to either not use the Regent air and get a price reduction for that. On international flights it shows business class, but a new twist allows you to pick premium economy and price reduction if you wish.
Oceania's 3 newer ships are close to Regent ships size, other than Navigator. they offer economy air, but you have to pay extra for excursions, premium booze packages, tips.
Booking a Regent cruise shortly after it shows up is really important to do right away. It is different on Regent.
The lower tier cabins are basically the same, They just cost more the higher deck you are on.
This is why they sell out so fast if you would like to save a little on the cabin price.