For completeness, I thought I would include the Monstrous Compendiums in my reviews of Dark Sun. There are two of them: the first is "Terrors of the Desert", the second is "Terrors beyond Tyr".
As pictured, Terrors of the Desert comes in a ring-binder format which might either entice you or put you off. Personally, I didn't care much for this format to be honest. I'd much sooner have a paperback book (or hardback, even).
Overall, the pages of the book are exactly what you might expect: a list of monsters to be used within the Dark Sun Campaign Setting. Statistics for these creatures are given in the standard 2nd Edition Rules set for AD&D (i.e. Climate/Terrain, Frequency, Organization, Activity cycles, Diet, Intelligence, Alignment, numbers, AC, mv, Hit Die, THAC0, attacks, damage, special attacks/defences, MR, size, morale, XP, Psionics, combat, habitat/society, Ecology).
The random encounters tables are provided at the front of the pages and are arranged by terrain (Verdant Belts, Stony Barrens, Sandy Wastes, and so forth) as might be expected.
The actual contents of the book consists of a large number of creatures. These range from the infamous Gaj which was potentially encountered in Freedom, through to drakes (earth, water, etc.), agony beetles, B'roghs, antloids, wild Kank, banshees and Athasian Giants. Of course, there are more than these, but that should be enough to give a flavour.
I found some of the domesticated animals interesting (Critic, Renk, Ock'n, etc.) as well as the the natural predators and unique Athasian undead (banshees are from Dwarves who have failed in their focus).
Overall, its not a necessary expansion, but one that could certainly add flavour and unique alternative opponents for the PCs to face. So its 3 out of 5 for this expansion from me. Nothing fundamentally wrong with it, and nothing terribly exciting either. It does what it says it will to be fair.