Aside from regular attacks, unit have certain abilities. A lot of the squads can boost their own power in exchange for becoming vulnerable to a type of damage (like Intercessors take more melee damage - but you want them out of melee range anyways, so that's nice). However, you can also get up to fun stuff like jet-pack equipped unit going on WHEEE rides not seen since Dawn of War. God, I love Assault Marines (even though they have less HP than Intercessors - maybe the studio hasn't gotten the "all Marines are now 2W memo).
