I use the DFDS ferry between Dover and Calais, usually on day trips to Northern France or Bruges.
Although the Euro tunnel is faster, the ferry enables me to have a meal, a drink and relax a little bit, which is always welcome on an otherwise frenetic day trip schedule.
In General, the Ferries are clean and well maintained, although lately it seems like half of the toilets are locked and out of action. The food on offer is basic but tasty, and the portions of a decent size.
Loading and unloading from coaches can get a little frenetic, with everyone pushing towards the stairways leading to the car decks, but I have learnt now that between docking and unloading is a good ten to fifteen minutes, so I may as well stand back and let the crowds disperse.