One of the few games that is built around 2 expansions: Starcraft 2. This game has a broad history and a strong storyline, which cannot be told in a single campaign. Aside from that, Starcraft 2 is still one of the most online played and streamed game out there of this moment.
The story continues in Starcraft 2, as the roots were planted in the first game: Starcraft 1. The storyline however is split up in to 3 versions and point of views: that of the Terran, Zerg and Protoss. The game came out as "Starcraft 2: Wings of Liberty" and featured the Terran point of view first. Now in the upcoming expansion we will see that of the Zerg (often also name 'the swarm', hence the name 'Heart of the Swarm'.
The campaign will be just a little shorter as that of the Terran, so you will actually get another ~8 hours of singleplayer gameplay (which is quite big for an expansion). It's confirmed this expansion will add approximately 20 missions, whereas the original game was released with 29 singleplayer missions. As I mentioned earlier, this time it will feature the Zerg point of view, and you will also be playing as Zerg. The continue picks up where it was left in 'The Wings of Liberty'. This time Kerrigan will have a leading role, as opposed to Jim Raynor.
The campaign will have multiple custom units included, which are not available in the multiplayer. They might also work differently or have different abilities in the singleplayer. There will also be certain upgrades available again which are not obtainable in the multiplayer, just as in Wings of Liberty (think of bunkers getting guns).
Then moving to the multiplayer. Starcraft 2 is still a job for many pro gamers, who earn their money playing in tournaments (with prices up to thousands of dollars) and getting sponsored. If something is unbalanced, these pro-gamers (who play at least 10 hours a game) will notice it immedeatally. This means Blizzard will have a big responsibility on their hands, the balance needs to be top notch like always. I must say that they did a really good job keeping all 3 races very well balanced, despite of all the different units, structures and abilities they have.
With Heart of the Swarm all races will recieve new units. You can see all the new units here. This of course is risky as the game needs to be re-balanced. Every unit has a counter, by each race. Blizzard will add new units to make the races more interesting. For example Terran will get more mechanical units, since in Wings of Liberty most Terrans would go with biological units. Protoss is getting more air units, as they have always struggled in that perspective. And so the list goes on, Blizzard is trying to make the races more fun, but also more balanced by adding new units. Each race received approximately 5 new units.
Another part of this expansion are the new multiplayer maps. Maps are a big factor in multiplayer games. Big wide open maps favour the Zerg race, however maps with a lot of small core doors favour the Protoss race (you get the idea). Taking all of this into account, there is a lot of work put into the maps to keep them balanced, and bringing them out in masses is quite the work.
I cannot yet tell if it's working out, as the expansion is still in early beta. Blizzard is still patching the expansion every other day to try to assure the balance is top notch. Certain units may be taken out, others might be added. Some units may be made less powerful, and other's may receive a boost in speed. Even after launch, Blizzard will continue patching and tweaking the game to ensure it will be as close to balanced as it can get. Blizzard has done this with their previous game, Starcraft 1, and also with Wings of Liberty. With this in mind, I have all trust in Blizzard to make the multiplayer refreshed and balanced in this expansion.
Now, how much will this expansion cost? There have been alot of rumours about this, some claimed it would be priced as a normal game. Here is the official answer from Blizzard:
"We typically don’t provide details about pricing until the game is closer to release. We do view Heart of the Swarm as an expansion set, so for the regions that have a standard box business model such as North America and Europe, we will price accordingly. For other regions that have alternative business models, we’ll provide details at a later date."
As you can see, it will be priced as an expansion. This is relatively cheap for almost a whole new game. Looking at the singleplayer, you will get quite a lot of content for the price. Looking at the Multiplayer, you only get some new units and new maps. These two balance each other out, and I think pricing it as an expansion is the correct choice.
This expansion will also modify the engine slightly to improve the graphical display. Blizzard said the following about this:
"We’ll be making some improvements to the graphics, including upgrades to the look and behavior of zerg creep, as well as some changes that allow our artists to better showcase the new types of planets that Kerrigan will explore in Heart of the Swarm. We still plan to keep the minimum hardware requirements the same for this expansion set as they were in Wings of Liberty."
If it's worth to get? Without it you will not be able to play the multiplayer anymore. And if you are not a multiplayer fan, than you can buy it to see how the singleplayer will continue. In short: If you liked Wings of Liberty, than this expansion is worth your money, from what we have seen so far.
Check out the HoTS preview trailer here.