My family (DW, DD, father, and stepmother) booked adjoining interior cabins on the Sensation for a 5 night cruise to Half Moon Cay, Freeport, and Nassau. DD is a first-time cruiser (she's 4. We'll forgive her), while DW and I have been on several, and my father and stepmother are experienced (Platinum with RCI, have also sailed Holland America and Carnival before). We were a little leery of the interior cabins and the general reviews of the ship saying it was "worn down" and "small."
Fortunately, it seems the reviews we read were wrong. Our cabins (4B interiors) were plenty spacious for all 5 of us to get together for pre-dinner conversation and wine for the adults (we bring our entire allotment of wine onboard, so we had 4 bottles between the 2 cabins). I could see it being cramped-feeling with 3 or 4 non-preschool-aged people, but even with the bunk lowered, getting around wasn't really a problem. From peeking into exterior cabins (ones left with the doors open!) while walking down the hall, it seems that our interior cabins were the same layout, the only difference being that ours had a false window. No biggie; the lack of natural light in the morning made it so dark that I actually slept in a couple of times (habitually, I wake up at the crack of dawn when not vacationing).
Our cabin steward, Wanwan, was gracious and accommodating for a couple of basic requests (wine glasses left in the cabin, and ice daily). He was thorough in cleaning for us -- the man even paired up shoes left around the cabin and placed them all together!
185 square feet seems small, but it's surprising how roomy it can be when it's well laid-out. We never really felt like we were on top of each other in the cabin; I could see it being a little tight if you've got 4 adults, but for 2 adults and a preschooler, it more than sufficed. R71 and R75 were nicely convenient to the fore elevators, but not so close that there was a ton of elevator noise.