terran are just too simple to play with, they don't have any notable weaknesses except there defences basically take unit space. but seriously, siege tank, bunkers, SCVs to repair (protoss are woeful in this area), stimpacks, there buildings can lift off making claiming new resources a piece of ****. battlecruisers are very very strong as well and the yamato gun outranges all defences making them a nightmare to deal with sometimes, the viking is unbelievably good (use them a lot due to their abilities), the banshee is unbelievably good as well (12 base damage, 2 attacks AND a cloak!).
protoss for example i have found to be far more fragile early game than the terrans, their cannons just get chewed up by light breezes and cannot be repaired, they have no shield batteries anymore, zealots seem tons weaker compared to the first game (seem to get chewed up!) and they still have their achillies heel, pylons (though its a great balance), later in the game if you survive all the pointless rushes they become probably stronger than the terrans, carriers are typically strong (especially if your enemy isn't ready to deal with them), the void ray has its uses and they get the most useful feature on the game, warp prisms and warp gates. units that are definately a miss for protoss are: the reaver, those were nasty things and i can't understand why they removed them, the arbiter (PLEASE BRING IT BACK!) and dark archons (mind-control anyone? maelstrom/psionic storm combos? feedback?) and the scout because lets face it, the phoenix is effectively useless...