Well, I've never been on the Fantasy...but I would enjoy the cruise myself. It depends on what you want to do on your cruise. The ship will have shows, pools, food, and all of the basic things you get on a cruise. It might not have the latest bells and whistles but it should be lots of fun.
As for money, if you are not going to drink more than one or two drinks and leave off the casino, you might not need loads of money. I usually look at the shore excursions I want to take and book/pay for them beforehand, which frees up money that I have when I board the ship.