This is the second or third version of this post, it's been sitting on my harddrive as I pondered posting it or not. It's a good chance to be utterly, completely and totally wrong as well as deeply unpopular with the hordes of Gillz who will treat Starcraft 2 as the second coming of Jesus; any criticism will be because you're a noob, you just don't understand or you're a fanboy of something else. This way I can get my licks in before the orthodoxy is unassailable.
Starcraft 2 will be huge, there's no doubt about that and will probably be the second best RTS game ever created. I write this because it wont be the best RTS game, we're getting Starcraft Lite rather than Starcraft 2 and the signs are there to read as to why. The obvious retort to this claim is the usual 'omg DUDE, it's a BETA, it'll get like WAY better' (many people who disagree with me come from California). Remind me- what was the last game that really changed through beta as opposed to getting a little more polished? There are stronger arguments against this, the issues with Starcraft 2 are systemic, they're not little things that fiddling a couple of numbers can change. The pieces of a game all interconnect in ways that mean you have to set certain ideas early in the design process and cannot shift the whole far from that afterwards.
The macro issue has been discussed to death on Starcraft forums but not everyone here will be familiar with it. In Starcraft 2 there are a couple of interface changes that will destroy the game's skill curve and many players, even very experienced StarCraft players have their heads in the sand over this because they've never been through the sequel process. They have confidence that depth will appear mysteriously in other places to compensate. This doesn't happen, depth is not magic, you should be able to explain its source and the reason for the way the interactions create depth.
The important changes are auto-mining and multi-building select. Automine means that if you rally (where the unit goes after it's been built) a worker production building to minerals the worker will automatically start mining after being produced. Sounds fine doesn't it? I mean telling every worker to mine is just so tiresome after all. This utterly destroys depth by removing the link between multi-tasking skill and macro. 100% macro is basically unattainable in SC and the slow improvement in macro has helped keep the game fresh, if after 1 year people can produce a little more at a given time in the game it can introduce cascades of changes as to which strategies are viable. It also changes the timing of many existing plays in the game, see? Explicable depth.
In Starcraft 2 top players will reach 100% macro very quickly, if they're investing in economy it will happen perfectly, even during fights and harassment, which is where perfect macro was hard before as you have to shift your view point to tell the workers to work in Starcraft. If you have four bases in SC2 that you want to produce workers you press your bases bind (all bound to one key) and hit the worker shortcut 4 times. That's it. Even low-level players will macro perfectly. Compare to SC's 4 separate binds, 4 worker shortcut uses then 5 view shifts (1 to each worker and back to where you were looking) with 4 orders to mine. The arguments for SC2's interface have been extremely facile- 'it's progress', 'it's needed for newbies' (because not being dumbed down has hurt StarCraft SO much so far) or the worst, because it dresses itself in the clothes of game design- that it's just unnecessary clicks, why don't we make it take 20 clicks for each worker? Is that depth, huh? It's a question of degree, we could make it take arbitrarily many or few clicks, up to completely automated after 1 click so there is no reason why the SC2 interface is the default choice that's sensible, they are arbitrary levels of difficulty set against how highly you value the ease of use. Any level of difficulty of macro must be justified on its own merits. SC's current system creates depth by doing the most important thing in game depth- it creates a trade off of a vital resource, and in this case it's one of the deepest trade offs in gaming because the resource is YOU, not an arbitrary sum the game hands out, it's your ability to multitask, your hand speed and your choice- do you focus on the fight, your harassment, your scouting or your economy? By killing this trade-off depth disappears down the plug hole with alarming speed and nothing to take its place.
The next counter-argument, which leads on to my following point against SC2, is that the depth will be recovered by having deeper combat, possibly in more locations at once so the game wil be more exciting. From what I have understood of SC2 this will not happen. Macro is being re-focussed back toward one base with a later expansion than in SC so there will be fewer fronts to fight on, on average. This is a subtle interaction though and I may be wrong, it macro may be as or even more rewarded, I suspect not though for the next reason. The powerful attacks that helped define SC- sieged tanks, psi-storms, reavers and EMP (the examples demonstrate the global design choice) are all being nerfed or removed. Powerful attacks are weaker. There are pseudo-justifications for some of this but the overall effect wil be awful, 'smart'-caster being the one justifying the reduction of psi-storm power (basically it's being made much easier to use en masse so they have to nerf it). What does this mean for the game? Giant clumps will be less vulnerable as there are no swingy attacks that punish it. Map layout will reward you less for good positioning (as in a small number of units will no longer be able to hold against a large mass, or at least to a much lesser extent). Games will be more boring as fewer expansions can be held (well positioned units will get steamrolled by the giant ball army so only 2 bases will be held at a time), the intention of greater interaction will, counter-intuitively based on the aim of changes Blizzard are making not happen. There will be far fewer comebacks as small positional errors will not be punished enough to change the game much, it will be more like Warcraft 3 where you build up and protect small advantages through micro and any real lead will be nearly insurmountable, grinding out a boring and predictable win with your giant ball army. Interaction will be reduced and we'll see far more Warcraft 3-like games of one expansion each, fight to exhaustion then get another expansion.
There are other things that flash giant warning signs about SC2's depth but I am in danger of Jamerioing. The one of Superunit Protoss Mothership is an absurd gimmick piece of game design that practically screams DANGER WILL ROBINSON about the designer's thought process (CORRECTION: said designers have now clued up and fixed this nonsense so I'll add a new one). The Terran Thor is another warning-'hey guys, it's a cool giant robot. We're not quite sure what role we're going to give it but it's cool so by gosh we're going to shoe-horn it in regardless'. Another change that hints at bad choices is the Terran ability to recycle bunkers and turrets for their minerals after using them. The main point of SC's depth is resource investment choice. If you can make your opponent build a bunker or too many turrets you get ahead. This significantly reduces the pressure on players to perfect placement and will give a very hard to balance late game boost to Terran (along with reusable expansions) where they turn everything they can back into money.
Starcraft 2 will be massive, no doubt, everyone will jump on it as the next serious Progame. It will be played out in two years but the incredible execution skill will distract many people from the fact that the game is no longer developing, it's the same fights, timings and strategies every time. If ever a game needed a promode from day 1 it's SC2. It wont get one, or it wont be accepted sufficiently in time, it'd require the Koreans to use it for it to catch on and we will miss out on the potentially greatest game ever made because of it. It's really sad to see one of the greatest game franchises ever made getting hit so hard with the newbie stick.
Edit: the most recent versions of the gameplay seem to indicate that Blizzard are aware of and correctly addressing a lot of these issues. I'm still concerned about the loss of power from siege tanks (which are reportedly still pretty useless) and Psi-storms as well as the mobility of jump units but we shall see. SC2 might even be better than SC if unit command lag is addressed along with a return of destructive unit power. And the title is just sensationalism. So there.