The term 'acquired taste' refers to an something which is not immediately pleasurable on first acquaintance, but which with perseverance becomes rewarding.  The example usually given in dictionaries, for some reason, is the martini.

Lying behind the notion of acquired taste is the idea that the taste we are born with is not necessarily the highest level we can achieve.  By careful training, taste can be developed or acquired.  Whether this represents a move towards a more refined level of appreciation, or simply a fossilisation of taste into prejudice, is open to debate.

Literature which is too easily accessible is clearly not an acquired taste.  Books we love on first reading very often fail to maintain their appeal over the years.  Writing where we have to work harder to begin with is more likely to prove durable.