Complex sentence: It features a list of tracks from their older albums before the come-back of the 1987 release "Suffer" and their second "Into the Unknown" was not included because of its drastically different style and unpopularity.
Split into simpler sentences: It features a list of tracks from their older albums before the come-back of the 1987 release "Suffer". Their second album, "Into the Unknown", was not included because of its drastically different style and unpopularity.