I find the ECML extremely dull for the most part. Also most of the Merseyrail Northern Line from Hunts Cross to Southport. Rather off subject but nothing will ever compare to a 48 hour coach journey from Santa Cruz De La Sierra in Bolivia to Buenos Aires in Argentina. After the first hour of "Oh wow, it is amazing, it seems to go on for ever" it quickly becomes "Oh wow, it really does just go on forever".
The view of the river, Tobacco Warehouse (and others) provide some relief between Moorfields and Sandhills. And further north you have probably the only stretch of railway in England where you might - just might - see Red Squirrel from a train.