Mothering Sunday is a much quieter, much briefer work than Waterland, but in many ways they share thematic drives. Both books focus on secrets and private relationships, but perhaps even more important, both books are discussing the nature of storytelling and the interplay of narrative and those secrets.
Plus, there's just something I find very comfortable in Swift's prose. It straddles the line in contemporary fiction between formal and informal diction -- stylish without becoming stuffy. Mothering Sunday is brief enough that it can be read -- and should be read--in a single sitting.