There were two main series of adventures set in Dark Sun:
Freedom, Road to Urik, Arcane Shadows, and Asticlian Gambit. Dragon's Crown fits this series better than the other (one major NPC from Arcane Shadows plays a major role).
Freedom is a great adventure for starting a campaign (and works pretty well as a follow-up to the adventure in the box set), leaving many loose threads on which to build spin-off adventures. The PCs can get involved with some factions in Tyr that can later help or hinder them in Road to Urik. Road to Urik does have some problems in that it involves some mass combat, and pushes the Battlesystem rules pretty heavily. These two are the most heavily related of the DS adventures.
Arcane Shadows, in turn, starts in Urik (it doesn't take over right where RtU ends - there's a novel in between) and leads the PCs back to Tyr (or at least somewhere close) while trying to evade Urikian forces. Asticlian Gambit doesn't have much to do with the other adventures in the series, and I find it pretty weak (it involves two sorcerer-kings and several "random dungeons").
Dragon's Crown, on the other hand, is my favorite adventure for any D&D version. It is big, and takes the party all over the tablelands - and beyond. They get to go silt-sailing, creep through Hamanu's palace, search an ancient fortress from before the Cleansing Wars, fight in gladiatorial arenas, travel to the Forest Ridge (and deal with man-eating halflings), face off with almost-mad thri-kreen, and stuff like that. While there are a few dungeons, it's a mega-adventure that's NOT just one big dungeon.
Of the other adventure series (Black Flames, Merchant-house of Am-ketch, Marauders of Nibenay - Black Spine and Forest Maker may or may not be sort-of part of this series like Dragon's Crown is part of the other), I've only read Black Flames. Frankly, Black Flames stinks on ice. It features a 22nd level dragon (defiler/psionicist) who presses the 3rd-level PCs into service to do some stuff, and as the finale said dragon faces off against one of the sorcerer-monarchs. It's just bad.
I have heard good things about Black Spine though, which features githyanki and githzerai.
As for the scanning quality, I think the quality is a lot higher on the Dark Sun PDFs than on many of the others. Dark Sun was part of the early ESD project, when they took care to OCR and do actual layout on the books to make them look like the originals. After a while they decided that this took too much effort, and made a half-hearted OCR, and put the text behind scanned images of the books. I think the DS box set PDFs weigh in at about 15 megs each, while the later Planescape box set PDFs (which has approximately the same number of pages and the same number of maps and stuff) are more like 60 megs.