The Avenue Verte is a great route to go on, but it remains only partially complete. The UK side is definitely the poorer of the two and in my opinion if you are a confident road cyclist then a route down to Newhaven on smaller B roads is ideal.
Once you are out of Greater London the views can be very beautiful but like anywhere you will always come upon the greyness of some built up areas.
As soon as you arrive in Dieppe, follow the (sometimes hard to see) signs to the start of the traffic-less part of Avenue Verte for which you will then be treated to around 40 miles of beautiful countryside views and a very mild incline.
This is the 4 day route I would recommend: http://london2paris.co.uk/routes/4-day-cycle-routes/#newhavendieppe