Don't believe the hype
I finished the single player campaign, and played multiplayer over the beta for 2 month. Here is what I think of it.
The Single Player Campaign:
There was a lot of hype around the fact that the Blizzard split the game in 3 chapters, as terrans, protoss and zergs campaigns. The pretext was the depth of the campaign scenarios and the many choices we have while playing them.
Well, once you finish Wings of Liberty, you don't find that much depth. In fact the story is dull. It turns around a few characters which are really not interesting. (only 4, or 5 main characters in a game that covers an entire sector in space? Seems weird. Specially that you don't see much crowd in the game).The scenario, the dialogs and the several plots have a hard time to make you believe that this is a Sci Fi game.
If you ask about the "choices that will affect the game" that you may have heard, well it's not a big deal. It's simply this: there are some side missions, and regarding if you do them or not, you will be offered some tech units that you won't have if you do not do them.
Also some RPG elements were taken from the "In Game", and put in "between games". (There are several stages you can visit in between games, for a few rpg elements). What I mean is that, the upgrades you usually do in game, are now available in between game to be permanently effective. So it's like taking something from the gameplay and puting it in between missions to give u the feel that's it's an RPG ability tree. (Instead of having Planetery Fortress researched in game, you research it once in the Armory between the missions and it will always be available).
Yes, in between missions there are several menus and stages in which you can visit the lab, bridge, armory for different upgrades. You can speak with some of the characters, consult them to hire mercenaries or upgrades, gather info about different units. It's fun, but doesn't really change much in the game, nor give you the feel of doing something useful and different than others would have done in matter of strategy.
Note that your decisions Never affects the story line. Also, for a Strategy game, it is interesting that SC2 has no strategy inside. You can finish the game, without having thought 1 second what to build and where to place it. The game tutorials you from the beginning to the end, making you feel more like a spectator than a player.
One good thing is that the missions are diverse and interesting. Lots of detailed and different events and aims to achieve. Something is always happening, so you never feel like you are doing the same thing twice or getting bored. (I guess this is to balance the lack of strategy). It's never boring, and there is not one mission aiming the destruction of the other faction, which is a good thing. (there were no destroy all enemies missions in the path I chose).
The story itself is boring and "complex wannabe". But it isn't. It's simple, it's dull, it's even more boring than a bedside story.
The Dramatization is not quiet done. We never believe that we are in war. When you play this game, you will feel more like you are playing Fallout 3 in isometric view than a Sci Fi RTS game. (Someone should definitely use the sc2 map editor to make a fallout game).
In conclusion, the single player truly doesn't worth 3 different boxset for a campaign. You can wait that the price falls or rent it, if you are not interested in it's multiplayer.
Graphics and Look:
The designs are great. And the graphics are really detailed. It's almost the cutting edge. (No tesselation, nor 3D which would be cutting edge). The work on the details is meticulous, and the atmosphere is really immersive. The different stages in between missions, the cinematics, even the menus are really reflecting a hard work on the details.
The zerg buildings are fun to be disgusted by. They really worked well on this one. Zergs finally feel like zergs.
Sound and Music:
The voice acting is good, but it feels old and odd. Nowadays we are more use to more realistic and effective acting like in Modern Warfare or GTA series. Each time a characters speaks in SC2, you feel like you are playing a game in the late 90's, early 2 tznds. The voice artists have a hard time to transfer you emotions, which are already hard to empathize with since the game hardly makes you believe that you are in space and at war with 2 different alien races. (All the game you feel more like it's a romantic space comedy between jim raynor and kerrigan).
Music is ok, it plunges you into the atmosphere, but no catchy tune will stick in your ears.
Original soundtrack: A few country tracks will give you the sensation of being a marine lost in space, which helps the game a lot. The soundtrack is one of the strong points of this game although they could have put a little more titles.
Sound effects are good, specially the zergs buildings and larvas are fun to explode just to hear the sound they make. Different vehicles, and weapons are easily recognizable by the realistic and flashy sound they make, which is a very good thing for a game.
The Gameplay:
This is the strong point of the game. The gameplay is intuitive and easy to adapt to. It feels like all other games should be played like in SC2. Many useful shortcuts help you to play swift and easily. The menus are nice to surf, and never bother you.
The Multiplayer:
No new races. No much to say about the Multiplayer. It's Brood War in 3D, with some new units you already saw in other games, like CNC3 and Dawn of War. Specially the Tripod, mastermind, zone troopers, mothership, devourer appeared here as the Colossus, infestor, reapers, and mothership. Some gameplay features comes from the dawn of war.
So no much to expect if you like advanced creativity and originality, but the multiplayer is fun if you are ready to settle for an improvement over BW. Lots of achievements, many battle options, 1vs1, 2vs2, 3vs3, 4v4, Free for all, etc... Since Starcraft was a great game, it still fun to play it in 3D with brand new graphics.
The balance in the Multiplayer is fine, but some races have much more options than others. In terms of strategy, well, the game feels more like a corridor map challenge like LOL and DOTA. As long as you have the right units the fastest way possible, it really doesnt matter what you do with the map. So it's more tactics than Strategy.
The Map Editor:
This is the reason why you should buy this game, if you like to edit games. The map editor is excellent. It give you way to create any kind of maps, scenarios, and even games which has nothing to do with RTS. While playing the Single player Scenario, you will find yourself thinking "well, they should have done it this way and.. wait! it can be done with the editor!"
So if you find any flaws in this game, Blizzard offers you the editor to fix it yourself, which is a good thing.
Verdict: For Online Multiplayer RTS fans only.