It’s hard to teach an old zergling new tricks, but in “Heart of the Swarm,” the long-awaited first expansion to the real-time strategy titan “StarCraft II,” the Queen of Blades isn’t taking no for an answer.

“HotS,” as it’s lovingly referred to by the game’s giant following, delivers a much-needed unit update with convincing gusto and much-improved storytelling. Each faction — the insect-like zerg, psionic and honor-bound protoss and human terran — gets at least two new units for use in multiplayer, and zerg gets to take a turn on center stage in the single-player campaign mode.

This update includes a fantastic, streamlined user-interface and much-improved in-game physics (unit death animations are the main benefactor). But the focus really comes down to two things: a much-needed unit mix-up for multiplayer, and a creative side quest expanding on the brooding plotline.

Let’s get the technical descriptions out of the way first.

For terrans, we’ve got three important changes: a new splash damage unit in the Hellbat, which morphs from the four-wheel speedster hellion; widow mines, mechanical units that can be dropped into precious mineral lines or be hidden in key spots for surprise damage; and lastly, a speed boost ability for medevac dropships.

Protoss get three new units, all airborne. A mother ship core that helps guard against early-game harassment from opponents; an oracle that’s great at early-game harassment; and the tempest, a long-range siege unit for late-game scenarios.

Zerg, the stars of the show, also get perhaps the most original type of additions: a swarm host, which digs into the ground and spawns endless waves of small attackers, and a viper — a flying unit that snags enemy units and pulls them out of position (think Smoker from “Left 4 Dead”).

As fun as it is to play matches with these new units, it’s still a little too early to tell how they’ll impact the game as a whole. As the various worldwide professional StarCraft circuits get more accustomed to new rushes, defensive postures and countermeasures, we’re sure to see some very out-of-the box thinking on almost every new ability and unit.

Therefore it’s more useful, from a critical standpoint, to discuss what is already evident, such as the improvements in the single-player campaign.

“Heart of the Swarm” weaves a very persuasive and enthralling revenge tale for the zerg Queen of Blades, Kerrigan. Though it does little to develop the overarching storyline of the StarCraft universe, it is a huge step up for character development from Blizzard.

Kerrigan, a human-zerg hybrid, finally tries to come to terms with the murderous rampage she’s been waging against her former race. Finally with her human wits about her, she becomes much more believable as she struggles with the loss of her lover (the protagonist from the series’ previous entry, “Wings of Liberty”) and her suffering swarm. It would be easy to ignore the morality of this series’ long and brooding plotline and just jump into “this is what I want, I’m going to take it” dialogue, but “HotS” takes a harder route. Kerrigan is a monster, for sure, but she’s also clearly devastated and losing her humanity along the way.

Still, the plot alone isn’t asked to carry the day. Just like it did with the previous game, Blizzard again takes the opportunity to go off the deep end with crazy abilities, units and choices in single-player. Each mission introduces at least one new option along those lines. Kerrigan herself is present in nearly every level as a unit in-game, as well. Along with your own tech tree, she grows more powerful with each mission, leveling and gaining unique abilities like a character in a role-playing game.

And while there aren’t as many side missions or diversions as there were in “Wings of Liberty,” “HotS” does show off some new possibilities with terran. Jumping behind the controls of a huge custom battlecruiser was extremely fun, and hopefully an inspiration for the thousands of mapmakers constantly working to bring their gameplay ideas to the “StarCraft II” “arcade” experience.

That’s the point, really. This “StarCraft” update is inspired, imaginative and well-told, and it’s a great jumping-off point for what’s to come — be it in the competitive scene, your own progression as a player, or for creative minds who just want to play around in the game’s editor. Blizzard has once again crafted a well-tuned experience. One that you’re surely already knee-deep in if you’re a “StarCraft” fan, and one you should definitely consider if you’re at all curious in the ways of the Swarm.

Bottom line: New units and abilities give “StarCraft II” a satisfying and much-needed facelift.

Platform: PC Online: http://battle.net/sc2 laney.sam@stripes.com

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