Updated Thu, Mar 25, 2010 by Cyrak
Medics & Firebats: Wait, what medics? StarCraft II has removed the StarCraft medic completely, drastically affecting the early game. Firebats are also gone, zerglings rejoice! These changes have completely changed the zerg vs terran game.
Ghost: The ghost has been slightly revamped from its original state. The lockdown ability is gone, but cloak and nuke capabilities remain. The ghost can now use EMP rounds and snipe. Snipe is a low energy ability that attacks an enemy for 45 damage ignoring armor - this is devastating against weak caster type units like high templar.
EMP has been taken from the now obsolete science vessel and been given to the ghost. Rather than completely draining shields it now does 100 damage to shields. It still drains all energy from targeted units. Now EMP also reveals cloaked units for a limited period of time.
Marauder: Terran's new early-game tank. Marauders are heavily armored space marines that deal big damage against other heavily armored units. These are built out of the barracks, but require a tech lab upgrade.
Marauders are mixed in with marines early on to form a deadly ranged force. These units have more armor than marines and can tank fairly effectively against melee units like zealots and zerglings. This unit is similar to the zerg roach, though less agile -- they also can only attack ground units.
Reaper: The reaper is a cliff jumping, rocket pack using, gun toting marine. These units are extremely agile and used for harassment. They also have an upgrade available that allows them to throw a bomb at a ground target that explodes after two seconds for significant damage.
Reapers have the ability to jump up and down cliffs, effectively bypassing choke points which makes them ideal for harassing mining units and structures. This unit requires a barracks with a tech lab to produce and can only attack ground units.
The early strategy of amassing a strong economy and teching has not changed. Terrans, with their ability to burrow their supply depots, can easily block their chokes - unlike in StarCraft where a properly blocked choke required intimate knowledge of each map. The choke block allows terrans to easily defend themselves from enemies with a minimal army while teching, however with banelings' ability to destroy chokepoints in a matter of seconds, and new cliff jumping units that bypass choke points this is a riskier strategy than it used to be.Terrans now will often amass a small early army even if they are planning to tech, maybe throwing down a bunker near their minerals as a safety precaution, whereas in Starcraft they could tech to factory units without producing a single marine.
The terran marine & marauder army matches up well against zerg roaches and annihilates zerglings. It also gives terran a strong counter if the zerg decides to go mutalisks. In this sense the dynamic is similar to original Starcraft, however the lack of medics, and the addition of the powerful roaches has made this early matchup in Starcraft II much more of a slugfest than the one sided matchup it was in Starcraft.