Spent a day on a friend's canal boat, not done a full trip: short answer is you better like the people you're with. They're not as cramped as they seem from the outside, but they're certainly not roomy, and power is limited to what you can generate, so you're not gonna be using lots of gadgets or watching TV.
On the other hand, if you're with people you get on well with, lounging around on top of a canal boat with some beers and/or joints, chatting shit while it floats along, can be wonderfully relaxing.