Castella is a kind of sticky, coarse-textured cake which is somewhat sweet and has no strong flavor. It is often sold in blocks or rectangular wedges and can be found pretty much everywhere in Tokyo including 100-yen shops that carry food, convenience stores, markets and tony department stores. Not only can you get this low quality cake pretty much anywhere, but it is frequently used as a base for a variety of other foods including rusks and filled whoopie-pie-style sandwiches. While no one ever force fed me castella, I was given plenty of it either in the office I worked in as a souvenir or as a gift because the assumption was that I'd love it because most everybody does in Japan (hence the reason it's sold all over the place). While it certainly is no blight on the food landscape, it's really not very good sponge cake. It's fatty, sticky, and somehow too dry all at the same time with insufficiently strong flavoring (like, oh, say, vanilla) to make much of an impact. It's like the mutant offspring of a loaf of Wonder Bread and a yellow sponge cake from a Betty Crocker mix.
I won't miss being given or gifted castella, and having to pretend that I liked it in order to protect people's feelings.