yes, this is hard to review. mainly because in some parts it's incredibly interesting, and yet in others, it's incredibly dull.
the speculative stuff - all about where, how and when humans may colonate the universe - is fascinating. i could read about this sort of stuff forever.
the dreary stuff, to be honest, is a series of chapters describing in mind-numbing detail about dust and mountains on mars. i read it - to be sure - but i regret the time wasted. i'll never get those hours back again.
still, for the good bits, this book rocks. it's quite nice being able to read with hindsight. sagan speculates that we will have colonised the moon in the early 21st century, and will be on our way to terraforming venus with microbes that will help make the atmosphere more habitable. the other bits, it could do better. hey, carl - hope you're enjoying the cosmos, man.