Although not technically part of the Dark Sun releases, the psionics handbook in one form or another turns out to be essential to all of the campaign. The reason for this is that every (yes: every) character in Dark Sun has access to psionic abilities to a greater or lesser extent. Some are full blown psionicists - a new class that is dealt with in detail in the handbook, whilst others are simply "wild talents". The wild talents are those born with some ability that they've learnt to master or use over the years. Levitating a chair, telepathically communicating with their Fathers, and so forth.
Almost every iteration of Dungeons and Dragons includes some kind of psionics. The second edition is probably the first most expansive description of psionics and its usage. But I don't think its the best to be honest.
Let's start with the positives. There is the psionicist class in and of itself. The powers that psionicists can use are detailed in several disciplines (psychokinesis, divination, telepathy, etc). And the class itself has a certain flexibility that makes it stand out against magic users (plus there's rules on what happens if psionics meets magical abilities that try to do opposite things). This is great. The sheer amount of new abilities is awesome.
On the negative side is the clunky implementation of psionics. This ranges from the rolls needed to activate particular powers (INT-some number that you can't recall, for instance) as well as expenditure of PSPs (power points used to power each ability that gets depleted until the user rests). I strongly prefer later systems that introduced MTHAC0 (mental THAC0's) and MAC (mental AC's) to activate abilities -- they were a good deal better iteration of the system. Moreover, every power has a negative side effect if a natural 20 (on a d20) is rolled. These tend to be rather extreme such as disintegrating oneself when trying to disintegrate something else. These are not fun! And why use them if you're not going to play to have fun? Further, the telepathic combat system is poor. It'd be much better if something like mental HP existed (or tangents as they are in later editions) before ID insinuation (and other negative effects such as telepathic domination) takes a foothold in the victims mind.
Overall, 2 stars out of 5. A necessary evil, but I strongly commend latter iterations of the psionic system to you to use in a Dark Sun campaign.