To me, Psionics is like the next step after Wizard to Sorcerer. The Psion gets another degree of freedom. The points system allows conversion between spell levels at the cost of spells known. The Psionic flavor has blurred over the years and now there are very few things you can do with magic but not psionics (turn invisible) and even fewer you can do with psionics but not magic (rebuild your character). I miss the flavor differences.
The biggest rules problem I had with Psionics is that the powers scale too well. The scaling is far better than any Arcane or Divine spell because a Psion can spend a couple extra points to give the power a higher DC. Also, there are no damage caps in place on Psionics. When a Wizard learns Charm Monster he knows it will only be really useful for a few levels and then it will slowly fade to worthless. The Psion never has that problem. My players would argue that the Psion is limited by number of points per day, but by the time they reach level 10 they never seem to run out of points. The 3.0/3.5 point system is like allowing the Wizard to trade all of his magic missles for another fireball.
The other issue I had was energy damage. Dragons are a lot less dangerous when your best damage dealing spell can be of any enrgy type (except acid, but very few creatures are weak to acid). Wizards and especially Sorcerers had to be prepared to cast weaker spells to get around enrgy resistance/immunity, but the Psion never has that problem.
To perfect Psionics, using 3.5 rules as a baseline: 1) I think that the scaling needs to be limited, or replaced with Magic-like per-level scaling. 2) I think that energy damage spells need to be separate spells and not just 5 cloned spells for each area shape. 3) We need to put the psionic flavor back in the psionic power list.
