The critical pieces are a mixed bunch. Marlene Barr's introduction is self-indulgent, complete with a photo of her meeting Buzz Aldrin, and rambles, grabbing all kinds of bits and pieces — she feels obliged to inflict on us, for example, some newspaper columnist's inane argument that Star Wars missile shield proposals are flawed because threats to "the I.T. cloud" are more serious.
Neal Postman's argument that we should look back at the 18th century for ideas "to take into the twenty-first century" is pretty superficial — and his potted history of civilization makes the egregious mistake of excoriating the ancient Greeks because "Their word for those who could not speak Greek was 'barbarian'".
Darko Suvin offers some interesting criticisms of Zamyatin's We, but his attempts to relate that to the fall of the Soviet Union relies too much on a single political tract (an Internet article by one Michel Chossudovsky). And Rosi Braidotti's piece "Cyberteratologies" remains readable despite drawing heavily on Deleuze and giving most of the big names of cultural theory a play.
I enjoyed other pieces much more, however. Marge Piercy's essay "Love and Sex in the Year 3000" looks at some possibilities for the future and surveys feminist utopias. In "Fiction Beyond the 21st Century" Patrick Parrinder classifies stories about the future, looking at the significance of particular dates and at differences between "near, far, and intermediate futures". And two short pieces use the same conceit to combine fiction and criticism: Eric S. Rabkin reviews two histories of science fiction written in 2999, while Kim Stanley Robinson tackles two histories of "science in the third millennium".
Other people's tastes will differ from mine, of course, but most will probably want to borrow Envisioning the Future from the library and read just those pieces that appeal most.