Do not expect the book to be serious or high brow. It’s silly, predictable and satisfying. Very satisfying if you are a geek that enjoys pop sci fi and fantasy culture. If you enjoyed that aspect of Ready Player One, then you are likely to enjoy Armada too. If that’s you, go ahead and read it, you’ll enjoy it and it’s short.
I feel the book could have spent much more time world building. Maybe Ernest Cline didn’t do that because, unlike Ready Player One, the world is supposed to be our own regular world; but there are a few technological changes that left me wondering how much more advanced it was. I feel that later on, when more information is revealed, a flashback with a lot of world building would have helped me getting more into it.
The audio version read by Will Wheaton is great. Most of the book is read in a more or less neutral voice but every now and then he makes appropriate voices (such as Yoda) which I find suit the book rather well.