After WoL's lousy storyline, we get a fantastic sequel thanks to Mass Effect 2's writer and Blizzard's gameplay design.
Well, here comes Heart of the Swarm, from now on referred to as HotS, to save the day.
Needless to say, this is a direct sequel to the previous game. Here we find Kerrigan recovering from her time as Queen of Blades, while Raynor collaborates with Valerian Mengsk, Arcturus' son, to topple down the dominion. However, Kerrigan's desire for revenge wiill spark a conflict that will consume more than just the dominion.
That's all that I will say about the campaign, since it is good enough to warrant playing it for yourself. Suffice it to say, plenty of loose ends from Brood Wars get tied down, and all the new characters introduced have a rich background, a purpose and a very distinct personality.
Gameplay-wise, the campaign kicks WoL's ass. HotS's host of missions are extremely varied, going from Infiltrating a protoss ship to destroying a secret lab from a very special character, along with all the gamut of destroying other bases and protecting objectives. There's even a mission where you can control the Hyperion in a sort of mini-game. Long gone are the tedious missions of gathering resources, or the hold the fort ones. Now your objectives are solid, even on the side missions, and the inclusion of "Evolution Missions" (missions that show you how a specific strain of zerg works) provide a very necessary respite of the seriousness of it all.
Graphics wise is much the same, with some improvements here and there, with the biggest one being improved physics, meaning a baneling bust will produce much more lovely giblets. On the other hand, aurally, Glen Stafford returned as music composer from Starcraft 1, which really makes for a huge improvement.
On the multiplayer side of things, there are enough additions to keep players occupied until Legacy of the Void. Not only there's quite a bunch of new units, but there have also been several improvements and modifications for old units, rebalancing most of the unused ones. Things are a bit tipped in favor on the Terran side, but nothing too bad. For a full list of changes check out Blizzard's homepage. I'll just say that multiplayer is as fun as ever, and even more so given the changes in UI, matchmaking and custom maps.
So far, Blizzard has managed to lift Starcraft back to it's former glory. If it keeps the course, Legacy of the Void will be a blast.