If you are a DDI subscriber, go login to D&D Compendium right now. If you aren't, this could be a good time to start. The first playable chapter of Player's Handbook 3 has just been released on the compendium and character builder, as promised. It shows the new Psion class, featuring the weirdest class mechanig yet seen on 4E. Psionic Power Points are back, there are augmented at-wills instead of encounter powers, and the D&D universe will never be the same.
Ok, maybe I got a bit carried away. But there has never been an exception to 4e's strict power system before. Amazingly, this might not break the game, after all. The basic principle isn't too complex: you start at level 1 with 2 at-wills and 2 power points (more on that later), gain an extra at-will and power points at level 3, and from there on, you get new PPs and an option to replace an at-will with another of higher level whenever you would get an encounter power.
Power points are used to augment at-will powers, enhancing their effects or damage. Several augmentations are listed per power, but only one can be used at any given time. The beauty of the system lies in the fact that at any given level, if you use the strongest augmentations available you get an equivalent effect to that of another class' encounter powers. And you have roughly enough power points to get as many such pseudo-encounters as the number of encounter powers other classes would have. So it's kind of a wash.
Except it isn't - there is the option to use lesser augmentations, which gives you unprecedented flexibility.
I'll make a more in-depth post on this topic one of this days. Meanwhile, here are a few cool compendium links (subscriber-only, I'm afraid), but you'd better check it out for yourselves.
Dishearten (at-will 1) - The ultimate controller at-will
Memory Hole (at-will 1) - Are psions pacting with fey?
Betrayal (At-will 1 ) - Reverse Commander's Strike!
Mental Trauma (Daily 1) - Despite power points, daily powers still exist.
Mind Blast (Daily 9) - Go Illithid on your enemies!
Dominate (Daily 15) - Guess what this one does...
Full Psion class description. My poor tooltips won't do the job here, just click on it.