This is one of the weaker books in the GURPS line, and I wouldn't see much value in it besides for the collector. It includes the alien creation rules, version 1, obsoleted by Compendium 1 and GURPS 4th Edition. After that, it includes 28 alien races, some from earlier GURPS supplements, but most new to this book.

Those races new to this book are usually uninteresting and poorly detailed. There's a race of evil snake people. There's a race of small furred creatures. There's a race of wise psionic rocks. I've managed to sum up almost everything the book has to say on those three races in three words each. Too many of these races depend on psionics or other super-science features for my tastes; many of them will only be useful for space opera.

It's not very crunch-heavy, besides the first couple dozen pages of rules; using in GURPS 4th Edition or other systems will merely require converting a racial template, which should be pretty obvious with or without much GURPS knowledge. My recommendation, instead of this book, is to combine GURPS Space (for 4th edition) with GURPS Traveller: Alien Races 1-4 (especially GT:AR4, as it has more races and ones that are less familiar to Traveller players). ( )