Ath'kethin
Elder Thing
As others have approached the level limits question, I'm going to focus on psionics.
The Complete Psionics Handbook has a completely different mechanic for running the abilities than the Skills & Powers book does. In fact, the Skills & Powers book was a deliberate revision to the 2e psionics rules, published in conjunction with the revised Dark Sun box set. The Complete Psionics Handbook is stil necessary for descriptions and effects for many of rhe powers, though (see below).
In a nutshell, the original 2e psionics rules, from the Complete Psionics Handbook, are a proficiency-based system, by which I mean the powers work, mechanically, the same way nonweapon proficiencies do. In the revision fouind in the revised Dark Sun box set and the Skills & Powers book, they changed it so that psionics work using the combat mechanics instead.
As mentioned in the intro to the Psionics Section in Skills & Powers, they eliminated the Metapsionics discipline. Some of the powers, such as Aura Alteration and Mind Bar, were moved to other disciplines, but many, including AFAICT Empower, simply vanished. The Psionic Power Summary tables, starting on page 175 of Skills & Powers, list all the available powers and indicates whether the power's effect has been changed in the book.
It was all confusing at the time and is still confusing now, since if you're using Skills & Powers you still need the Complete Psionics Handbook (as well as Dragon Kings and The Will and the Way, bith of which are Dark Sun supplements) for descriptions of many of the powers. Of course, if you're cool with the proficiency-based mechanics, you can just use the Complete Psionics Handbook (plus the two Dark Sun books if you like).
The Complete Psionics Handbook has a completely different mechanic for running the abilities than the Skills & Powers book does. In fact, the Skills & Powers book was a deliberate revision to the 2e psionics rules, published in conjunction with the revised Dark Sun box set. The Complete Psionics Handbook is stil necessary for descriptions and effects for many of rhe powers, though (see below).
In a nutshell, the original 2e psionics rules, from the Complete Psionics Handbook, are a proficiency-based system, by which I mean the powers work, mechanically, the same way nonweapon proficiencies do. In the revision fouind in the revised Dark Sun box set and the Skills & Powers book, they changed it so that psionics work using the combat mechanics instead.
As mentioned in the intro to the Psionics Section in Skills & Powers, they eliminated the Metapsionics discipline. Some of the powers, such as Aura Alteration and Mind Bar, were moved to other disciplines, but many, including AFAICT Empower, simply vanished. The Psionic Power Summary tables, starting on page 175 of Skills & Powers, list all the available powers and indicates whether the power's effect has been changed in the book.
It was all confusing at the time and is still confusing now, since if you're using Skills & Powers you still need the Complete Psionics Handbook (as well as Dragon Kings and The Will and the Way, bith of which are Dark Sun supplements) for descriptions of many of the powers. Of course, if you're cool with the proficiency-based mechanics, you can just use the Complete Psionics Handbook (plus the two Dark Sun books if you like).