The Minotaur is a heavy unit with no critical spot and shields only vulnerable to arc damage. If that's not enough you'll have to be at least level 15 to actually kill one. If you get close the Minotaur will teleport to you'r location and melee you either killing you instantly or taking out 75ish% of your health. Armed with a high damage low velocity explosive rifle they do tons of damage. Hobgoblins, as depicted above, are more long range enemies. They are armed with a high velocity high damage they can kill you in one hit, and when shot they will activate a momentary shield that makes them resistant to everything.
Harpies are a flying enemy that will attack when you get close enough. They will open their sides and start shooting you with three separate guns dealing low amounts of damage quickly. Finally we reach the Goblins which are the lowest class and the easiest to kill because they have no shields and have very low power weapons. The only reason that they should be able to kill you is because there were too many .
Destiny is a complex game and these are the enemies worth fearing because they can do so much, so get out there and kick some robot butt.