I thought Bioware changed the overheating system because it made ME1 too easy.
With the right assault rifle (that really expensive one from Spectre Requisitions), some level 5 thermite rounds and a level 5 heat sink you can really break the game.
I still preferred the overheating system though because you could whip out your gun and spray people, windows etc on the Citadel and not waste ammo.
I find it really strange that every single gun uses the same clips, from a tiny pistol to a HUGE Widow sniper, one little tube cools all.