Starcraft 2 beta: Okay so I've been playing this enough now to rant.
First off, the long wait. Blizzard has been delaying SC2's launch (what a shock) mainly for the implementation of Battle.net version 2, which I have to say... is completely justified. The new matchmaking system is miles better than what we used to have for B.net.
Essentially, when you first start multiplayer, you play a series of placement matches that determine which league you fall into. I'm not sure on the specifics of who it decides to match you up with, but it's presumably random. After this, you're placed into one of four leagues (Platinum, Gold, Silver, Bronze) and a division. Each league has hundreds of divisions, and each division contains a pool of 100 players. All normal matches are ranked on this ladder and you move up and down in ranking (and in league, if you manage to do that well or fail that badly) and your games henceforth are always found with someone of as near a skill level as possible.
Games actually denote on the loading screen who's favored (which is a feature I have mixed feelings about), at least in terms of ladder rank. The amount you move on the ladder is determined by how good your opponent is relative to you, so beating someone who's considerably favored above you will get you that much higher and vice versa. Note that you still will get matches with players outside of your division (and also presumably out of your league if you're on one of the extreme ends of the division).
What this all boils down to is that it greatly neuters the issue of skill level disparity. SC1's greatest obstacle to a lot of people who would have otherwise been interested in playing is a massive skill gap to be remotely competitive with the 'average' player. This is in no small part due to the game's age, but Battle.net's game setup offered absolutely no idea on how good your opponent/teammates were other than a nebulous win-loss record. In addition, that whole issue of joining lobbies and watching a dozen people join and quit in the process is now in the past. Finding a game is literally one click and wait. You can even state map preferences so that you can avoid matches on maps that you dislike, if possible.
As for the gameplay itself, it really comes off like a modernized version of SC1, doing away with some quirks that some people may miss, but most will prefer. For example, the nightmares of unit pathfinding are no more - the AI for movement and unit grouping now is almost impeccably good to the point where you don't really need to micromanage your armies anymore. Little touches like being able to rally workers directly to the mineral resources so that they start auto-mining instead of having to individually assign them to harvest keeps some APM pressure off of players who can focus their attention on the actual strategy of the game. Things like rally points don't suck anymore (units actually engage enemy units en route rather than getting shot down like idiots), and you can (FINALLY) group more than just 12 units when highlighting them! It's even easy to effectively micromanage a large group of mixed units with different abilities because you can tab through each unit type in a group to access something, like setting a bunch of tanks into siege mode and then tabbing over to stim your marines. I have little issue with the interface, although new hotkeys require adjusting to and it does take a bit to recognize the new art, buildings, etc.
As a result of all of this, I feel like the game rewards overall economy and macro considerably higher than individual unit micro and tricks that SC1 lended itself to. Attack-move tactics, while not 100% optimal, still pretty much do the job most of the time, although you still need to control things like casters and abilities in general to get the most out of units. You can also get away with playing a lot more defensively, although it's still not ultimately a winning strategy (can't defend your way to victory, after all), although it's also much much easier to do things like "drop army into opponent's main" due to a number of new options made available to all the races.
The game also runs amazingly easy and is not remotely spec-heavy. I know friends who manage to run the thing on laptops (albeit on the lowest settings), and my four-year old PC can run the game on maximum settings with absolutely no issue.
The races themselves are, although the same in spirit, pretty changed in execution from what they originally were in SC1. This is probably a bit out of scope for most people reading this but I'll get into a bit of it anyway to give an idea of what's different:
Terran - arguably the easiest race to play now in a complete reversal to their SC1 counterparts. Bionic builds are solid and have a place in almost every matchup (TvP and TvZ in particular, while TvT still lends itself more to mech/air play), despite Marines not getting a single base boost. This is because groups of marines aren't retards that go off and get themselves uselessly killed anymore due to the new improved grouping and pathfinding. The Marauder, another Barracks unit that replaced the Firebat, is also solid and is almost universally used in any infantry group. Meanwhile, tanks still exist, they have the most versatile air options of all the races (an anti-air flyer that can transform into a ground attacker, a medic transport, cloakable air-to-ground harassers, etc.), and they're still probably the most efficient race in resource:unit potential overall. Their unique macro mechanic, MULEs, are basically super-SCVs you just fire and forget from your Orbital Command.
Zerg - is probably now the most complicated race to play. People either love or hate Roaches, the new T1.5 unit that bridges between lings and hydras. They have a lot of units that require good micro (roach burrow, baneling targeting, infestors) and still emphasize flanking armies like nothing else since all the familiar zerg traits are still there, like ling speed. Rather than hatchery spam left and right, Zerg now utilizes Queens built from hatcheries that can accelerate larvae production, which is their unique macro mechanic. Overlords no longer detect (lol), as it's now a Lair upgrade that requires morphing them into Overseers. Creep mechanics were greatly expanded on - all Zerg units run much faster on creep (significantly so for some units) and spreading them is no longer a matter of just building hatcheries and colonies, but Queens can actually produce Creep Tumors (which are self-propagating, and can make more of themselves) and Overlords can generate creep as well. This also comes with Nydus being T2 rather than T3, which can lead to hilarious cheese potential.
Protoss - Cheese, cheese, cheese. Protoss got a serious change in the form of Warp Gates, which are a Gateway upgrade that's accessible once you research the tech at the Cybernetics Core. Warp Gates work like this: instead of queuing and building a unit normally, the Protoss player can instantly warp in the desired unit into ANY location on the map that's currently in range of a Pylon power grid (with a 5 second warp-in time), effectively eliminating build wait time. Instead, the Warp Gate then has to go through a cooldown that's equal to the build time of the unit that got warped in. Essentially, it frontloads unit production by giving them instantly but making you wait to make more. It's the ability to have them appear literally anywhere next to a Pylon that's full of BS potential (to make it better, their transport can temporarily generate a Pylon power grid, which means you can fly one over into an enemy base and warp in an army that's only capped by how many Warp Gates you have built). Or proxy pylon, or any number of various things. Their macro mechanic is Chrono Boost, which is a caster ability off of the Nexus that speeds up unit production/research/whatever's being worked on, on any building of their choice. The most basic use of this is to simply pump out more Probes ASAP, but it of course also speeds up army production or getting critical techs you want done immediately.
In summation: I highly recommend anyone who even vaguely enjoyed SC1's gameplay to pick this up when it comes out (it is a Blizzard product and you should do that by default anyway, but this bears saying). The skill ceiling has been lowered considerably and the multiplayer is now vastly more accessible regardless of how good you are at RTS games. All the normal issues that plague beginners (forgetting to build/idle workers, pathfinding, unit grouping, AI in general, etc.) have been readily addressed, while there's still plenty of depth and the overall metagame still flows like the original Starcraft. It's also faster paced to get going, which is a good thing since most SC1 matches tended to last 5 minutes minimum just to get to the point where you could actually mount any offense other than a rush. Blizzard has gone out of their way to make sure even people who think they suck at RTS to have a fair shot at each other, and consistently playing against people on your own level makes the game immensely more fun.