I have the CapitalOne credit card and use it every chance I can. I have found it to be more worthwhile to accumulate the points toward money off rather than a free cruise. The free cruises are limited in their sailings and cabin categories.
It takes $23,000 to earn $500 off a cruise , or go to $46,000 for a $1,000 certificate. I have already used a $500 cert. and have enough points for another one, but will probably let it ride up to $1,000. You have 5 years to accumulate points. The key is to use it for everything possible. I have only had mine for 2 1/2 yrs. I always pay it off at the end of each month so they are, in effect, paying me to cruise.
There are also other uses for the points, such as upgrades, fruit baskets, etc.