Normal is baseline.
Veteran they get a bit harder, use powers more, etc.
Hardcore every enemy will have at least a weak Armour/Shield/Barrier layer, along with improvements from the above.
Insanity gives them much stronger Armour/Shield/Barrier, even more damage, accuracy and health and makes them more agressive with better teamwork.
Basically the jump from Veteran to Insanity is gigantic and if you are finding the playthrough easy on Veteran, switch to Hardcore to get a feel for the enemies with the extra layer of protection since it screws with the vast majority of powers.
Insanity is best left for a brand new playthrough since it'll be harder when you start off (no upgrades, lacking some guns, no squad loyalty, no points unelss you newgame+) and make for a better challenge than jumping onto it for the last few missions at full power.
Veteran they get a bit harder, use powers more, etc.
Hardcore every enemy will have at least a weak Armour/Shield/Barrier layer, along with improvements from the above.
Insanity gives them much stronger Armour/Shield/Barrier, even more damage, accuracy and health and makes them more agressive with better teamwork.
Basically the jump from Veteran to Insanity is gigantic and if you are finding the playthrough easy on Veteran, switch to Hardcore to get a feel for the enemies with the extra layer of protection since it screws with the vast majority of powers.
Insanity is best left for a brand new playthrough since it'll be harder when you start off (no upgrades, lacking some guns, no squad loyalty, no points unelss you newgame+) and make for a better challenge than jumping onto it for the last few missions at full power.