More like 4.5, maybe even 4 (the writing wasn't fantastic or anything, and he definitely could've delved deeper), but I learned a ton of cool information, so that bumps it up.
For the sometimes complex subject that he writes about, Perkowitz explains it in an easy-to-grasp way. Of course my favourite part was when he talked about cosmic foam, but the whole thing was quite a fun enlightenment on bubbles and foam.
I always thought it was fun to play with, and now I can marvel and wonder at how it is so much more.