Hi Robbo,
Rouen depends on what time you are there, its the most direct from Calais, horrid in rushhour, depends how lucky you are at other times.
Last time I tried a alternative route, it was slower that banging through Rouen.
One alternative is to leave the A28 at J11, pick up the A29 to Le Havre, exit at J9 Yvetot and cross the Seine at the Pont de Brotonne, when you get down to the A13 you can either pick up the new motorway to LM, the A28, or carry on to Bourgthroulde on the D313 and pick up the N138.
Are you on the bike or in a car? Suspect the former, don't forget there are apparently no services/fuel on the new motorway yet.
If you want more details on the Yvotot route let me know.