Published 20 years after the original, this sequel may seem like a has-been author's desperate grab at reclaiming the magic of his best seller, and I was trying hard not to see it that way. The beginning didn't help; it's supposedly set less than a year after the original, but it feels like more time has passed. Technology has jumped to include cell phones and the Internet, and the main character is somehow in college. Okay, Barney's age in the original was never specified, and in this he's a high school student who happens to work at a library at Harvard, so technically it could be only a year later (like 14 - 15). It just doesn't feel that way. Also, Barney makes some very deliberately poor decisions at the beginning that really don't match his character.
There's actually a valid reason for those decisions which is revealed later, but the beginning could have been written better to foreshadow it. Maybe going meta, where Barney kind of knows he's making weirdly bad decisions and he knows better, but somehow they just feel like the thing to do. Anyway, the story picks up quite a bit, and goes where a sequel should: Barney goes on an adventure and this time makes it into space. His life is even more endangered than in the first and the situation is complicated enough to be interesting but still makes sense. Many of the original characters make an appearance, and the sequel concentrates on some even weirder aliens.
It's a bit funny to read the author's note at the end, which describes how he came to be a little obsessed with parasites right before he wrote this story. He doesn't say this, but I imagine that his willingness to kill off characters and exile the Pig means he's not wanting to write any further sequel.