Feeling Conflicted About 40k Rules Sets

I've been wondering to myself lately about the things I like about Warhammer 40,000 8th edition and what I liked about prior editions.  Specifically I'd like to play with my Horus Heresy-era stuff, but I can't seem to bring myself to go back to how 7th Edition WH40k played.  I'm not sure if it is because I felt like 7e was work to play, the players I played made it feel onerous, or if I'm genuinely dissatisfied with how it worked.