Well, then what is it in this band? It's different to me then what I'm used to. I usually don't like slow soft stuff.
Post-punk is basically when punk: (1) decided to become more introspective/personal and less political, and (2) slowed down their punk rock riffs, and experimented with other genres (including dub, psychedelic rock, krautrock, funk, electronic, disco, musique concrete, jazz).
Post-punk is really broad, and includes subgenres: goth rock, industrial noise, EBM, noise rock, dream pop/shoegaze, synthpop, minimal wave, coldwave, no wave, neo-psychedelia, jangle pop, etc
Post-punk isn't always slow.
But it can be (and when it is, it's often known to be cold, detached, somber and/or melancholic)