I actually got this stuff. It has me interested in 4e now. I think they did a very good job.
I like the Campaign Setting being sparse. After all, you only need enough to give the feel and then the DM should do the rest anyway. I don't want them to tell me too much, because then I'm constrained.
I'd have preferred if they left Kalak alive to be taken out by the PCs. That would have been more interesting.
They also didn't give stats for Tithian or whatever his name is. The King of Tyr. He's just a mortal schlub... of course you need his stats! If the PCs want to take over a city-state, well, here's iron-rich Tyr with its huge ziggurat and everything controlled by a creampuff; why go over to Nibenay and jack with that hero-stomping half-dragon sorcerer king when you could just lay this local clod out with your bronto-bone truncheon and call it a day?
Unless it assumes that King Tithian is actually nice and the nice old PCs won't want to take him out. Wrong-o. That is very un-Dark Sun.
In general, though, it seems full of awesome and win. The creature book seems to rock, although I'm not in a position to critique 4e mathematics.
Oh, Marauders of the Dune Sea is pretty stupid. It amazes me that WOTC, owners of Dungeons and Dragons, and having access to both a budget and the internet, is unable to find anybody who can actually right a coherent adventure. It's pathetic, really.
Overall, I had to reward WOTC with my custom for actually publishing Dark Sun. It's not that tired old "generic fantasy" stuff, not even with a twist. It draws on the rich traditions of sword and sorcery and sword and planet. It is a worthy setting and I think that overall WOTC appears to have done a worthy job with it.