Maybe more like 4.5/5. 
 I usually prefer longer works, but I appreciate Chiang ' s talent for brevity. this is one of those works that would have bogged down had it been any longer than it is. 
 As other reviews have already noted, this is a book of ideas, from software obselescence to ai ethics. When does an artificial lifeform gain rights? To what extent? What are the ramifications of discarding a sapient personality when it's engine is no longer supported (even if the entity would be unaware of the passage of time)? Can we apply morality and ethics to the virtual world? 
 And, of course, the side commentary on engagement with software over reality, but what is 'real' anyway? 
 Needless to say, I liked this book. On a personal note, I'll also admit that I got a certain amount of cheesy nostalgia out of it. The digients reminded me of advanced versions of the Norns from Creatures (anyone else remember those?)