Wiktionary
cult hit
n. 1 Something (almost always a film, book, song, etc.) which is very popular among a specific, narrow audience 2 Something (almost always a film, book, song, etc.) which is very popular, and which was popularized by a specific, narrow group of fans
Usage examples of "cult hit".
ST:TMP reaped its own economic rewards, and quickly became both a cult hit for obsessed SF geeks and a reliable summer blockbuster.