StarCraft II has more of an emphasis on the single-player campaign, and it’s much more fleshed-out than the single-player in the original StarCraft. There’s more of an emphasis on story, with a lot more in-game cutscenes, more dialogue during the missions, bonus objectives in each mission, in-game achievements, co-op missions that can be played as single-player missions, and difficulty levels for the campaign. Brood War doesn’t have any of that.
The combat units have seen upgrades and evolutions across the board as well. Overall, there’s a big emphasis on upgrading your units. You earn money from every completed mission, which you can use to upgrade every unit in the game, as well as some buildings, and your ship. Not to mention that completing side missions and collecting pieces of Zerg and Protoss technology gives you access to even more upgrades.

The unit-pathing in the game is a massive improvement from the original StarCraft. It makes moving a lot of units from point-A to point-B much less tedious. When combat units attack on their own, they obediently return to where you originally put them. Having combat units not be able to contain themselves, jumping into combat on their own, and getting themselves killed isn’t an issue like it was in the original StarCraft.
The difficulty has been scaled back from the original StarCraft. Many of the levels will introduce a new combat unit, and the mission objectives serve as a tutorial for the player to learn how to use that unit. Warcraft III did something similar. The single-player emphasis is less on sharpening your tactics, and more on teaching the player the mechanics of the game.
By the time you finish the Terran campaign, you’ll have a good feel of how everything works. So if you’re feeling adventurous, you should be ready to play some multiplayer matches.

Mission objectives are much more varied than the original StarCraft. There’s more to do than build base, build and upgrade army, scout for enemy base, use army to destroy enemy base, rinse and repeat. There’s nothing more fun in any of Blizzard’s RTS games than blowing stuff up, and there are missions in Wings of Liberty that are dedicated to turning you loose and letting you do that – and it’s really, really fun.
What was also impressive is the lack of linearity. As you progress through the campaign, you have multiple missions to choose from that you can do in any order you like, and there are a whole set of Protoss missions to play as well. This serves to help mix things up and give the player an appetizer of what’s to come in the Legacy of the Void campaign. Also, there are two spots where you get to determine what course the story takes by choosing to either help or fight certain other characters.

(If you haven’t played the original StarCraft, there will be minor story spoilers from it in the rest of these impressions.)
Speaking of story, as always, Blizzard’s CG cutscenes are top-notch. In Wings of Liberty, the story centers around Jim Raynor as he continues his revolution against Emperor Arcturus Mengsk, while dealing with the guilt of what happened to Kerrigan in the original StarCraft. He has his friends Tychus the marine convict, his engineer buddy Swann, Matt Horner, Dr. Ariel Hanson, and Dr. Egon Stetmann as his allies.
Some of the story beats were prophetic regarding what is going on in today’s world. Seeing in-game billboards that encourage civilians to inform on their neighbors, and that proudly proclaim that ‘obedience is safety’, sounds strangely reminiscent of what we’ve been hearing from certain politicians during this pandemic.

StarCraft II predicted fake news years before Trump became president. They have in-game cutscenes featuring a galactic news network called UNN peddling fake stories and lies about Jim Raynor and his rebellion. The undercurrent of social commentary was eerily familiar for a game that released ten years ago.
VERDICT
Overall, I love the improvements Blizzard made to the single-player campaign of Wings of Liberty. The game feels much more tailored for StarCraft fans who love the series mainly for its story, lore, and solo missions, rather than being tailored for fans who immediately want to test their mettle in the trenches of Battle.net.