Master of the Desert Nomads. Like its predecessor, it presents a mix of wilderness and "dungeon" challenges and, also like its predecessor, it's not wholly satisfying taken solely on its own merits. That's why I prefer to think of these two modules as two parts of a greater whole. The whole is not without its problems, but I think there's enough good about it that I retain a fondness for modules X4 and X5, the last Expert-level modules for which I can say that without significant qualifications.
Both Temple of Death and Master of Desert Nomads are products of the "new," more mainstream TSR Hobbies, as evidenced by the change in trade dress, corporate logo, and artwork style from earlier entries in the X series. Of particular note is the growing tendency of modules and rulebooks to be illustrated by one or maybe two artists in order to give it a "unified" appearance. While I can see the logic in such an approach, it can be risky, especially if the artist chosen is not one you personally favor. Such is the case in module X5, whose artist is Timothy Truman, whose artwork I've never held in particularly high regard, even less so in the fantasy genre. Even had I liked Truman's work, there's a sameness that comes from having only one artistic vision that I think weakens the product.
Temple of Death sees the characters make their way through the tunnels of the Great Pass into a series of valleys that lead to the land of Hule, where the evil Master rules. Cook really pulls out the stops when it comes to the encounters of the Great Pass. There's a mechanical dragon, a palace of hallucinogenic fungi, and a moon pool, among others. Many of these encounters could spark mini-campaigns in themselves, particularly the moon pool, which, on nights of the full moon, generates a ladder to the Moon itself. It's terrific stuff and reminder (as if we needed one) that David Cook's imagination is steeped in the lore of pulp fantasy.
Hule itself has always read to me like a fantasy version of Khomeini's Iran, with the Master substituting for the Ayatollah. It's an evil theocracy, where clerics rule over all, though we're not given much information about what this theocracy believes or why. It's a common problem in the D&D line: religion is treated as a potential source of controversy, so it's generally ignored, despite the presence of clerics. Now, granted, Temple of Death, as its title ought to make clear, was never intended to be anything more than a fantasy adventure, so I've never been too broken up about what it glosses over. Still, I think it's an opportunity missed. Moreso than Master of the Desert Nomads, the action of module X5 takes place within a "dungeon" location, the eponymous temple from which the Master rules. It's a large, heavily-fortified complex filled with a variety of evil spellcasters, guards, and monsters. Surviving to face the Master should prove a difficult endeavor for a party of characters level 6-10, especially since the Master has several tricks up his sleeve to ensure that, even in defeat, he might still carry the day.
As a kid, I liked Temple of Death better than its predecessor by a wide margin and, while I still think I prefer it of the two, I don't think it's the hands-down superior choice that I once did. Part of it comes from the fact that I think Temple of Death's reach exceeds its grasp. The characters must enter an evil theocratic nation, find its leader, and slay him -- all in the span of 32 pages. That's a tall order for any module and I don't think Cook succeeded in fulfilling the promise module X5 seemed to hold before I'd read it. In addition, there are still worrisome instances of heavy-handed NPCs to nudge the PCs in the right direction and ensure that events go "as planned." I've certainly seen worse examples of this shtick, but that does little to exonerate Temple of Death's use of it. In the end, I think there's still a lot to recommend this module, though I'd rework a great deal of it if I ever chose to run it today.