I've been playing the beta and I'd just like to write down my thoughts on some of the units that I've been using. I don't care for posting my blog on forums but I'll try this once. If someone's already gone through with this feel free to just lock it.

I have little to no experience with a lot of RTS games. At least playing competitively, recently though it's all about online gaming for me and I'd just like to share some of my views on the units I've been using. I try to play as all races but I've seen that I win more games playing as the Terrans. So far my strategy has changed from an armada of siege tanks in SC1 to a harassing/stealthy airborne attack force in SC2.
 

• The Marines are my general unit. I use them to kill off most of the enemy's force or at least to lure the enemy away from my reapers or vikings.
• The Marauders support my marines by blowing away the bigger units and I think these guys slow the enemy down after an upgrade. Will check but I wouldn't recommend playing a game without these guys.
• Reapers are essential to my game since I like to focus on ripping the opponents economy to shreds without a huge battle. Some use Hellions, I think Reapers are far more efficient.
• I haven't been able to use Ghosts as much as I would like... here's hoping that will change so i can start dropping nukes and play my stealth game.
• Vikings are one of my favorites especially against Protoss players (overlord hunting is hilarious with these guys). I love their hit and run capabilities. I get a lot of flak for dropping in and then flying out after destroying an expansion.
• Medivacs are dropships and I use them a lot to fly my marines and marauders around. They also heal your units which is a plus but they don't heal as quickly as you would like. Wish they had an ability to lay down a healing AOE ability to help with standoffs.
• Ravens are science vessels on crack. I love these things since they're also amazing for harassing. Auto turrets and seeker missiles make these guys a pain in the ass for the opponent. They require a lot of micro but I recommend you practice with these guys.