We did it on our honeymoon in December, and also loved it!! They give you blankets, since it can be a little chilly at night. But we just snuggled up together and enjoyed the ambiance and moonlight. Wonderful and very romantic for a couple.
On the other hand, I haven't experienced it as a group, but as we were waiting for the carriage ride, we saw a group come back from theirs, and they were laughing and joking and having a great time with the driver. So I think it's safe to say that you can have a fun time too as a group, not just a couple!