Hi-res sprites fragmented explosion support. Soldiers & alien units can explode like weak monsters in Baldurs Gate.
Aliens' and soldiers' weapons sent flying if their owner drops & dies.
Tanks can explode to pieces and bits can be seen bouncing around also back from floor and walls.
Bouncing sparks & ricocheting bullets, new explosive effects: walls coming apart and pieces flying around.
Crater support.
Fallout 1 gooification support aliens spitting quick-dissolving molecular acid into soldiers faces causes XCOM soldiers to be dissolved alive like in ALIENS.
Large structure collapse support. Multi-storey buildings coming down from explosions and behave like an old house-block during demolition.
Impact hits: soldiers are thrown back if alien is too strong and hits them critically during melee. Similarly sectoids can fly backward from a healthy slap given by a Schwarzenegger Commando.