I haven't played or seen the Dark Sun series to comment on it. Though from images they seem rather similar to the Ravenloft series. At least mechanically.
The first one is pretty excellent, imo. It's probably my personal baseline for "This is how a party-based cRPG should
play" and the storyline and whatnot wasn't entirely terrible -- I have a pretty much eternal love for the dark sun setting because of that game. Pretty heavily recommended if you can stand playing that era and style of game, heh. Engaging combat for that time period, rather interesting setting that lends itself to a quite neat magic/ability system (relative to the time, at least, and imo) and some non-standard races (thri-keen!), just a bunch of really nice stuff.
The second one I've tried to start and stopped very shortly after several times... something about the graphics just throws me off really bad, makes it hard for me to play. Supposedly it's largely the better of the two, though, if more unstable, iirc.
They're mechanically pretty much nothing like the ravenloft series, though. They're top down, heh, among other things. E2: One of the reviews actually nails it pretty well -- the two games are pretty close to the immediate precursor to Baldur's Gate. Entirely turn-based instead of real-time w/ pause, but otherwise definitely in the same vein (or rather BG is in the same vein as Dark Sun, heh).
E: Also jeez, those reviews on gog. It seems people agree with me :V