Hi renegade10005, and welcome to cruise-chat.com.
I do suggest that, as this is your first cruise, you book through a travel agent that specializes in cruises. But, finding a deal over Christmas is going to be difficult. This is one of the prime cruising seasons. As for cabins, what are your needs? Veendam has a variety of cabin choices, everything from interior cabins to a penthouse suite. I've stayed in both an outside cabin and deluxe verandah suite, and there are benefits to each -- of course, the suite has far more.
As for reviews -- you're always going to find a mixed bag. I often tell people that if I had paid attention to every negative review, I would have missed out on what turned out to be my favorite ship.