I though the higher APM was a lot due to the fact that Zerg simply makes more units. But I never play with Zerg, so...

I play random, and Zerg is very difficult to play compared to the others. A lot of it is due to being forced to use the queen to spawn larvae, and the generally weak zerg units.  Ive found the key to zerg is to rush hard and dont let up, if the enemy gets too many units, zerg gets destroyed.  You also have to do a lot of tricky shit just to keep the playing field level.  You have to flank with zerg units, or they stack and get eaten alive. 

And terran infantry still eats zerg alive.  Its a tough race to play, and I think it is slightly underpowered.  But not hugely.

I just gotta say I am loving this game. I am replaying the campaign for the achievments. I have a few more playthroughs on Hard and Brutal before my ego is satisfied and I delve fully into multiplayer.

As for the differences between the races, I have played a couple games against the AI and have noticed a few stark differences:

1. The amount of buildings needed to create all units (tech buildings,add-ons, command center, hatchery and nexus excluded):

Terran - 6 total building. Source: http://us.battle.net/sc2/en/game/race/terran/techtree

Protoss - 9 total buildings. Source: http://us.battle.net/sc2/en/game/race/protoss/techtree

Zerg - 9 total buildings. Source: http://us.battle.net/sc2/en/game/race/zerg/techtree

2. Zerg feels and plays different than SC1

First, they nerfed the Zerg mobility off the creep, which I surmise mainly due to the devs thinking players would make heavy use of the Nydus Worm. Second, the moving up of the hydralisk as a tier 2 (Lair required) unit makes very little sense ontop of the movement speed nerf the hydralisk received off creep in SC2. Third, the spellcasters for the Zerg are completely underwhelming to say the least. Finally, the Zerg AOE damage units are few and far between (Baneling is tier 1 and Ultralisk is tier 3).

3. Terrans get their bread and butter with 3 buildings

Marines, Marauders and Medics come at the cost of a 50 mineral/25 gas tech lab add-on to the Barracks. Zerg and Protoss need to drop double the amount for their bread and butter armies. Furthermore, the siege tank can come fairly early.

4. The Protoss Sentry can be gamebreaking

The Sentry's forcefield ability can effectively wall-in opposing players so that they cannot expand. If used on ramps, you can absolutely divide and conquer opposing armies.

5. Zerg is the only race who has to Tier up their hatchery to have access to all their possible units

Hatchery (Tier 1) costs 300 minerals, upgrade to Lair (Tier 2) is 150 minerals and 100 gas, and upgrade to Hive (Tier 3) is 200 minerals and 150 gas. Neither Protoss nor Terran have to factor in these sunk costs when playing. Quite unfair to the Zerg, but not unexpected.

I would add more, but I am still observing and learning. Or as they say at the SC2 forums "What do you know NOOB! You are not Diamond, therefore your opinion doesn't mean diddly squat!"

"3. Terrans get their bread and butter with 3 buildings

Marines, Marauders and Medics"

Medics don't exist in the multiplayer, for healing you have to make a factory, starport and medivacs.

Also, if you want both marines and marauders you need at least 2 barracks with 2 different add-ons.

im currently playing some 4vs4 and i hate being with noobs. when i was supply 200/200 and had a huge carrier/stalker army one of my allies only had marines, and the other was at 200 supply with void rays and stalkers but he had no upgrades!!! so then i go and attack, i beat the armies of 3 players but then a massive viking army comes and destroys the rest of my carriers. and while im rebuilding my allies get owned by dark templars. they had scans but they didnt use them, they had observers but they didnt use them.

oh and let me mension that one of my allies left early on.

in the top 200 players most were terran. and the sad part is that MMM is effective against many builds, i think that it takes more skill to play zerg then terran. i started off as a terran player, then went to zerg, i had an extremly tough time playing well, expanding and having enough resources, now i play protoss, the noobiest of terran players can win a zerg player. they wall off so you cant do an early rush. they dont expand. and they build a 5 layer wall at mid game. every time i do an attack i have to destroy the walls so i can touch his units, but by then his siege tanks would have rapped me. when i go mutalisk/corruptor and then get brood lords i kill his tanks but then im faced with 100 missle turrets.

There are reasons to QQ about Zerg but losing to a non-aggressive Terran who's one-basing reflects more on you than the match-up.  Just surviving to midgame without severe econ damage from fast double hellions or tech-swapped cloaked banshee openings is a bigger concern.

FWIW, I main Zerg.

im in bronze league :P. he doesnt hurt me, but when its time to win i come with ultralisks brood lords corruptors, all my upgrades are done and i attack, and he manages to win with marines a 5 layer wall and hundreds of missle turrets. i know i can approve but it pisses me off how it takes more skill to play zerg.

You could try a Nydus Worm or Mass Overlords drop. His 5 layer wall will look ridiculously useless when you drop tons of units inside his base.

what part of one thousand missle turrets dont you understand. my only hope is mass brood lords but i stopped playing as zerg. i just played a one on one game protoss vs terran, i early rushed with zealots and destroyed his base, but he had an expansion and when i went to finish him off his command center flew off with 5 suvs, i tried to kill it off but i coudnt, i barely had one a couple of stalkers. so after that i played a game of cat and mouse with him for the next 30 minutes, he had atleast 3 command centers in the air, i had units at every single mining site, and i had void rays all over the place. but then he gave up after 30 minutes!! it was annoying as hell.