As Donna said there is no way you could even compare the two ships.
I sailed Inspiration in 2009 , it's a small ship by today's standards and has no bells and whistles. If you go looking to compare it with Oasis you will be very disappointed but now knowing that their two very different ship there's no reason you can't go and still have a nice time. As Donna said its what you Make of it.
Also keep in mind that other than Allure no ship that I know of can be compared to the Oasis class of ship, their a destination in themselves.
ALLURE, 2/21/16 *Last Gang Cruise*
Carnival - Fantasy 1998
RCCL - Majesty of the Sea 2000
Carnival - Inspiration 2009
Carnival - Freedom 2011
Carnival - Liberty 2013
Carnival- Breeze 2014
Sweet Escape BVI Charter 2015