The SCV's afterburner is now colored red and orange according to the April Fools Tauren Marine assaulting a Terran base.
In the concept art, they stay true in size and including every tiny detail set place on the textures. Especially the Tauren Marine's vandalism on his own armor.
The current Zergling have their wings shortened a bit.
The Marine has a new updated portrait according to the savior vs terran video. The Ghost no longer have that placeholder portrait from the Terran Advisor, they actually look like Splinter Cells now. The Zerglings have an updated portrait as well. Both Zerglings and Marines portrait seen on top of the website in www.starcraft2.com are outdated (Which I why I changed my avatar).
The Zerg creep expands asterisk style when the hatchery is built, then once finishing the asterisk, it completes it to a complete circle.
Main Menu may be a placeholder but it shows the bridge in the Hyperion. The "Menu" during in-game is now shorter and placed top left corner instead having it huge and right in your face. The same goes to players that are lagging, it's a lot shorter but still remains in the center.
If your screen is close to a nuclear explosion, but not looking at one pixel of it will reveal sun like rays from that direction. Very similar as to where you're getting hit from in FPS games such as Unreal Tournament, Halo 3, Call of Duty, and such but instead those are red marks on the screen.
If you order flying units to this direction but you want it to fall back, it no longer instantly in a quarter of a second to turn around. Like the Alpha and Beta StarCraft, they will turn around slowly. According to the warp rays and mutalisks.
Units may have different attack animations according to what they are attacking. For an example, the Ultralisks attacks Marines, Vikings, Medics, Siege Tanks and so on by swinging their kaiser blades. But when the Ultralisks attack buildings, it uses the classic attack style from the original StarCraft just more instant.
Unit death animations depends on what attack they're receiving. The Marines have a lot of death animations, from a standard death, shot through the head by Ghosts, cut in half by Dark Templars to even a complete splatter to explosive or from very high damage.
Though mentioned by Blizzard, Sunken Colonies and Spore Colonies returned with a new twist.
The pregame lobby has vastly improved. Not even WarCraft III improved that much compared to the original StarCraft. The lobby in SC2 are divided in three sections. The chatbox is still at the same area but a bit larger. The map name, screenshot, information, or maybe 'Author of the Map' is right above the chatbox. And above that one is a list of players, even though it got a lot shorter, smaller fonts and squishing each line in fits enough for at least twelve players. The "Start and Quit" buttons are at the same spot. Also, the countdown has been removed, it immediately starts the loading screen.
Chatting during the game is no longer on the left area of the screen, it's right above the area where you type and send the message.
None.