Hardcore Starcraft: NES-style: no saving. If you lose a mission you have to start over from 1-1, the first mission of the human campaign.
Battletoads Starcraft: The non-base missions (like recovering the psi amplifier) are much less forgiving about where you can move units without sounding an alarm and getting swarmed. You have to move and react quickly and precisely in order to stay undetected. For example, perhaps a guard unit would trip an alarm in 3 seconds, and so requires 3 or more marines firing in unison to be killed quickly enough.
Casual Starcraft MP: The game is officially and without exception banned by the South Korean government.
Hardcore Metroid Prime:
-All beams have limited ammo (including the power beam), and once out of ammo for all beams you have to punch things instead. Punching doesn't do much damage.
-Limited space for expansions on the suit, so you have to choose certain combinations of health/missile/powerbomb/ammo ones, and you can only change at save stations.
-Bombs, power bombs, missiles, and charge combos all damage you. Bomb-jumping just got a lot harder.
-No more charge-tractor beam.
-Damage from phazon also causes permanent mutation/corruption.
-Save stations don't heal you anymore.
-Enemies don't drop pickups (only crates and whatnot)
-No gravity aboard the frigate.
-Suit upgrades are now suits in themselves, so you can only have one at a time - Gravity, Phazon, or Varia? Again, they can only be changed at save stations.
-With the plasma beam you can melt all the ice in Phendrana Drifts and burn the plants in Chozo Ruins/Tallon Overworld.
-Limited oxygen in some areas - deep caves (Magmoor), underwater, outside the Frigate at the beginning.
-Magma is deep enough that you sink like water. This is a bad thing. Phazon is also found in liquid form.
-More stuff can be scanned. And must be for proper completion.
-Enemies repopulate semi-realistically, instead of reappearing every time you move two rooms over and come back. There are also, however, many more of them to begin with. And you can drive species extinct in any given area.
-You actually have to evacuate the Impact Crater like you would any
true Metroid boss area. It's also bigger.
-Better AI for basic grunts (like Space Pirates), and they now mob you in larger groups.
-You can cripple the Space Pirates' infrastructure, however, which decreases their numbers gradually. Much like extinctifying things.
-The suit gradually loses functionality as it loses energy.
-Once you run out of energy, you have to take off the suit and use that weenie little pistol from Zero Mission for protection.
-Status effects: acid burns, catching on fire, and so on.