The Desolation has a very cool and unique concept, the Wurm Riding ability (I even named my character over the Dune books thanks to this ). But so far it has been the most frustrating area of the game, thanks to what I consider to be a few problems there. The problems, and my suggestions to fix them, are:
1) In the "The Alkali Pan" map, at the Ressurrection Shrine at the south west of the map, the Wurm Spoor is too close to the rocks. This means that, in a full Hero/henchmen group, when you click on the Spoor to summon a Wurm, some of your heroes and henchmen will enter the Wurm and instantly will then leave it - since they're close to the rocks. You'll end with part of your team in a Wurm, part of it outside, and no way to make those outside to summon a Wurm other than leaving and entering a Wurm again.
My idea to fix this: it's not hard, in game, to command your henchmen to stay away from the rocks with the flag command, and then summon a Wurm. It's also annoying to being forced to do this...I would suggest simply moving the Wurm Spoor a bit farther away from the rocks (like in all the other Spoors). This would solve that problem.
2) The enemies: some enemy groups are balanced to be fought by the Wurms. One example of this is the group of Awakened beings. It includes a lot of enemies that are a challenge once you're inside a Wurm, but that are nearly impossible to kill if you're out of them. There are some points in the game where you are forced to fight these enemies out of a Wurm - for example, in the middle to north area of the Alkali Pan, you'll find a group of those standing above a Wurm Spoor. You cannot summon a Wurm until you kill the enemies, you cannot go there in a Wurm since it's right after a rock formation, and you cannot kill them without the Wurm...There's a similar problem in the Joko's Domain area, to the east of the Bone Palace entrance, where such a group stands in the middle of a rock formation.
My suggestion to fix this: move the enemies a bit so they're in the sand (in the Yellow Sand or sulfurous sand), far from the rocks or the Wurm Spoors.
Someone could argue, "c'mon, it's not that hard to kill them without a Wurm". Unfortunately yes, it is. The typical group has:
2 monks, with a ressurrection spell. This is a challenge, but isn't too hard.
2 paragons, with a ressurrection "spell" (the Signet of Return, a reusable ressurrection). This, together with the monks above, make it kinda hard to keep an enemy dead - even if you target one of those, the other 3 will ressurrect it.
2 or 3 mesmers with Cry of Frustration (an AoE interrupt that interrupts everything) and Hex Eater Vortex, a spell that removes a hex from the target (making hexes less than useful), does AoE armor ignoring damage, and removes one enchantment
1 necromancer with Well of Shadows (giving your attacks a 50% chance of missing - this isn't evade or block, something plenty of attacking skills counter, but rather a miss)
2 rangers with Debilitating Shot (takes away 10 energy per hit on you) and, above all, the worst skill in the lot - the Sandstorm elite skill. Thanks to this Nature Ritual, each time you attack or use a skill, you lose one energy, even if you're far from the spirit (as in, the enemies are in between you and it)
2 Dervishes with Vow of Silence (immunity against spells)
2 warriors to finish you off
This group of more or less 10 enemies is not a challenge, it's a source of frustration. A group with heroes and henchmen cannot defeat them without Wurm control. Add to this a boss (such as in the Alkali Pan, where this group has a Paragon boss helping it) and the fact that this group is linked (no pulling part of it away - it moves together) and you get a massive number of deaths.
3) The Wurms lack a reliable healing. It's funny to say this about characters with 3.000 health - but it is true. Against some enemies this isn't a problem - the worst the Margonites can do is put health degeneration on you, but as long as you're not taking too much damage you can deal with this. The problem are the other enemies, such as the sand elementals, that do 150 or more per hit. They cannot be knocked down, so the secondary main healing doesn't work...What bothers me is that, if a Wurm in my group is taking damage, I have therefore no way of preventing that wurm from dying.
My suggestion to fix this: add a "...and heals target other allies in range" condition to one of the skills. It would only heal allies, not the caster (so it wouldn't change anything in the Challenge Mission, where you're alone anyway), and it would help a player to keep his group alive.