Starting Town Halls automatically Rally to Minerals, & starting Workers also follow that rally. Town Halls don't automatically Hotkey or build Workers, though /sarcasm.
EDIT 1: SCV Build button has been moved down 1 square on the grid. ...OK.
Warhounds move faster than Marine / Marauders. They seem pretty beefy, too.
Hellions come out in Normal Mode out of a Reactor Factory, contrary to an interview where I've heard they're supposed to come out in Battle Mode (so it's since been changed, or perhaps out of a Tech Lab Factory they come out in Battle Mode). For me, the Battle Hellion attack flame animation is missing.
There's a sound menu option for Group Sounds. Balls of troops make new sounds (Marine marches, Mech ground-shaking, etc).
I hate how the Warhound looks, but it has a cool melee attack animation - it smacks things with its shield-arm. Same attack stats, I'm assuming.
EDIT 2: Holy moly, Terran Mech destroys Zerg WotL-current metagame. Terrans wanting to try Mech will build some Battle Hellions, which make Zerglings a joke - but the surprising part is that Warhounds fare very well against Zerg as well. Zergling-Infestor or Mutalisk-Infestor just melts against Mech with assisting Marines.
From a completed Match's results page, there's a shortcut button to Quick Match. Saves a click from before.
The workers mining instantly seems to provide a very minor mineral boost in the beginning for those of you like me whose game freezes for a second after loading up, thus making it impossible to control your Workers that first split-second.
Played some TvP's. As expected, Warhounds are frigging good against WotL-current meta Protoss. Notably, Zealots mess up Warhounds. The Warhounds' faster move-speed than MM means they end up in the front, where Zealots eat them; Battle Hellions move slower, and end up in the back, where they can't defend. So Mech requires good positioning micro, which is good balancing.
Important Note: There's an option (default off) to allow selecting Units not in your control. The reasonable assumption is that it prevents selecting neutral creeps. But it also includes enemy buildings, AKA warping-in Protoss or Zerg Structures which would otherwise be impossible to distinguish during their construction!
Battle Hellions don't do as well as expected against Zealots, versus Normal Hellions; they kill a little better, but not by much.
Warhounds don't fare as well as expected against Colossi. They do damage but because they're bigger than Marauders and not as fast with Stim, they don't do the job as well, IMO. They're probably better-suited for sustained engagements.
Fuck Oracles. They shut down mining at such a range that you could have never seen it at all. One or even two turrets per mineral line isn't enough, with that cast range, and regenerating shields.
Tooltips seem not to be functioning when hovering over Unit Build buttons.
Widow Mines no longer have a time until detonation. They latch on & explode instantly. Like SC:BW Vulture's Spider Mines, it's possible to detect them, and, upon triggering their chase, lead them a bit. They do friendly splash damage.