Starcraft 2 plays like old RTS games. You could criticize it for not keeping up with the times, but is that fair? No.
Does it fill them? Yes and no, that depends on your viewpoint. If you wanted a new game like Starcraft, you got it. If you wanted another revolutionary title? Well, you got it. But not on the gameplay front, so if you expected revolutionary gameplay, you didn't get it, and of course Starcraft 2 will, and is already, receiving considerable flak for that.
Starcraft 2 feels like the RTS's of old. You have 3 factions, they harvest the same 2 resources, and you need to use these resources to build a base and units, and then use these units to destroy the enemy base, harass your enemies, scout the map and so forth. It's the sort of gameplay that RTS's have gone away from.
Some people are going to say that that makes Starcraft 2 feel really old. I disagree. In fact, I think it makes Starcraft 2 feel very different. There just ain't any other games out right now that plays like Starcraft 2, and I missed these sorts of games. That sort of gameplay is what I like in an RTS, not what you get in the current gen.
So Starcraft 2, by being "old school", actually stands out. To the best of my knowledge there hasn't been a game like it since 2004's Armies of Exigo. If you enjoyed the original Starcraft or Age of Empires, Command and Conquer and other such games, there's a really good chance you'll enjoy this one, too.
All the 3 factions are really unique and really well balanced just like in the old game. Not all units feel useful, however, but most of them definitely get a spin.
Your choices are:
Terrain - Solid base defenses, building extensions with unique powers, all units are ranged, medium unit cost and power.
Zerg - Infestors. Uses creep, expands all over the map very quickly, builds forces from their hives very quickly, low unit cost and power.
Protoss - "The heroic aliens". Uses power grids, psi forces, and many other mysterious technologies. High unit cost and power. Bases take very little space.
You'll never be held back in your quest for intergalactical multiplayer dominance because you chose one race or the other. They are all powerful!
But of course, Starcraft 2 is not revolutionary in that aspect. This all sounds a lot like the original Starcraft, and that's because the Starcraft 2 core game is exactly like the original Starcraft with some UI twists, upgraded graphics and some new units - and that's it.
Starcraft 2 is unique in it's single player campaign. 26 missions with free choices between lots of missions, cutscenes between every mission, and the "bridge". This hasn't been done before in an RTS, and it's done very well. Every single SP mission I've played so far has been unique, fun and engaging. And I play on Brutal difficulty levels, which actually makes the game kindda scary. When the zerg attacks, you really do feel swarmed. There are hundreds of them, in a particular mission tens of thousands of them!
But where Starcraft 2 is revolutionary is in it's online. When you want to play ladder games, you just select your race, select your gametype, optionally invite people to your party if you want to play 2v2/3v3/4v4, and you hit a button and bam. You're playing in seconds, and the action is intense and team-oriented. (unless you picked 1v1, obviously)
Almost every match is a fair fight. Starcraft 2's matchmaking system is just absolutely positively amazing. Besides the preliminary matches, I haven't had an unfair fight yet. I win roughly 60%, slowly progressing, and yeah. It just works. And I've played more than 100 games of Starcraft 2 (in the beta as well)
Then there's the custom games. This is where the revolution is. Starcraft 2's editor is immensily powerful. You can import your own units, structures, models, ideas. You can change the entire user interface, make direct keyboard controls and basically construct any game you like! I know they call this a map editor, but if you know how to use it, you can create your own entire games with it. First-person shooters, puzzle-games, arcade games, you can change all the races, create several game types for the same map, create mods for the entire game, all from the editor. So in the end, it's a lot more than just a map editor - it's a game editor.
Oh, and by the way: Support for up to 14 players, not 8.
When you're done with your map or mod, you can just upload it to battle.net directly. When people are playing the game, they can search for any word found in the map's name or description, and they'll be able to download your map and host it. No need to go to any external sites at all. The map is then listed on the server browser.
Yes, you got that right. The map is listed. The server browser doesn't list servers - it lists maps. No more seeing a server browser with only DotA on it. DotA will take one maybe two spots on the list. The maps are sorted by popularity.
You can also update the maps and everyone who plays your map will then download the update the next time they wish to play it.
If you want to join a map where all the games hosting it are full, you'll be offered to host yourself. If you want to play with particular people, the supports friends and invitations, and even invitation requests.
Soon, you'll be able to sell your maps, and create world-wide ladder rankings for them, too!
This is a completely new way of doing online custom games. A big props to that, and a big reason why I give it a 9.5.
Besides, the production values are amazing. It didn't cost 100$ to make (Blizzard said a bit amount of those money were spent on World of Warcraft), but you definitely get something for your money.