We are not seasoned cruisers having only been on four cruises - the first three with P&O and the last with Costa.
The price we paid for our inside cabin was very reasonable - however it was discounted still further by Iglu cruise because we booked an outside cabin but were allocated an inside. Iglu cruise said this was an error but I strongly suspect that they sell you anything to get your booking and then work out what they can and cannot provide. Not an acceptable business practice in my view - but that is an issue with Iglu Cruise and not (possibly) with Costa.
The bad points first.
Larger than our inside cabin on P&O Oriana - but it did stink of cigarette smoke