I've been playing rpgs for over 2 decades now, and only got into GURPS pretty late in the game. I wanted to do a psionics-only gameworld and when I found this book, I got everything I needed.
I am a Gurps V3 Revised person (haven't looked at Gurps V4), but this book keeps me from wanting to upgrade to V4.
Pulver is one of GURPS' best writers, in my opinion, and in this book, he has thought out so many cool things for you to use as a GM (or as a player). Particularly what I like is a section called "Advanced Psionic Techniques" that takes all of the psionics powers to the next level, namely, letting you use the powers in tandem with other powers. Things that PCs will want to do, such as use Clairvoyance with Telekinesis to screw up enemies' internal organs -- there it is. How do Telepaths join up in a Gestalt and combine their powers? There it is. Overall, the rules work well to create a balanced world.
Some powers are obviously better than others. It is a shame that Pyrokinesis and Cyrokinesis are less useful (and just harder to apply in the game world) than Telekinesis. But as a GM, tweak a little here and there, and all of the powers become pretty viable.
The campaign worlds suggested by Pulver are all intriguing -- take bitz of what you will. The new advantages/disadvantages as well as drugs and cybernetics all make this book useful in the long term.
I've been running my psionic campaign now for over six months and I still have my players enjoying this world. I recommend you get the SUPERS book to use alongside it in case certain psionic powers (like Pryokinesis) need a little cinematic push (in that case, let the player buy Fire Ball, Flame Jet, etc.).