I was also initially quite excited about the entire environmental themed series, but after reading this and Frostburn, the "cold" book, I'm not so sure. Wizards of the Coast's authors have the unviable task of trying to write a generic book that's still interesting and flavorful. But, because it has to be generic, they can't go too crazy with the flavor that they do add, or it won't be as useful to players around the world. In this case, I think they went so far the other direction, that they've also become relatively useless to players around the world.
I've recently read several other RPG books that are compatible with 3.5 and have a desertish theme; the Katapesh and Osirion books from Paizo (and I'm reading a third, the Qadira book, right now) and Monsternomicon II by Privateer Press. Which isn't strictly speaking a desert themed book, but it happens to have a lot of desert related stuff in it. Those books are great. While technically specific to the settings for which they're published, in reality, they're useful because they're so good that I want to use them. Sandstorm, on the other hand, leaves me very little material that I'd care to use.
It introduces two new races; a humanoid race who's whole schtick is that they can swim underneath sand or other loose soil, and hippy goblins who live in the desert. I didn't find either of them particularly compelling. The prestige class line-up is similarly strange; either too generic to be interesting, or two unusual to be useful. A guy who specializes in riding on horse-sized burrowing worms, for instance... what do I do with that? Or a character class who's all about building sandcastles and other weird sand form sculptures, and embuing them with magic? Or a river guardian, who's clearly stuck in one very constrained geographical area for all her abilities?
There were a few monsters that were interesting, and it's always nice to have stats for more actual, regular animals here and there for us low-magic folks, who think stats for camels and jackals might be useful, but otherwise, they also came across as merely desert skins thrown on top of other existing ideas rather than stuff I can turn around and use right now. The "dry lich" for example; do we really need a dry lich, who's thematically and mechanically not really all that different from a regular lich?
The adventuring sites near the end were also really bland; your typical Valley of the Kings style pharoah's tomb, and desert necropoli, and stuff like that. Nothing overtly bad, just... nothing that really fired the imagination.
TSR used to have a couple of really interesting desert themed settings, including Dark Sun and Al-Qadim (Dark Sun in fact being slated for a 2010 re-release for 4th Edition) so there's a rich legacy to tap here. Instead, we're treated to nothing more than watered down D&D Egypt. I confess I'm disappointed.
I'll still go on to acquire (and read (and review)) Stormwrack and Cityscape, and in fact I've still got high hopes that the latter is the best of the bunch, but so far the environmental sourcebooks have struck me as a better concept than an actual product; an exciting idea that didn't quite turn into what I would have liked to see.