The complexity is in the combat.by Mischief Maker 07/15/2018, 4:52pm PDT
It takes into account weapon types (laser cannons murder tanks but underperform against infantry, melee and flamers ignore cover, etc.) number of live units in a troop, hex terrain both in terms of damage mitigation and line of sight, overwatch attacks, active and passive skills unlocked through research, and lots more.
It's not the math headache that Warhammer Armageddon was, nor is it painfully awkward and ugly like Sanctus Reach. It's the best 40K game to come out of Slitherine and I'm not alone in that assessment: