Brave new world was good, but theres plenty of sci-fi out there thats much better, its only good cause its a classic imo.
Enders Game was my favourite for a long time, but its hard to judge what makes a good book, wether there is social commentary, some sort of big philosophical message, how well they construct their universes, the little touches of tech like how they handle FTL travel[if they have it at all, some books go the route of cryogenic sleep and settle with lightspeed]. Ender's game was great, but it just doesnt encompass all that much.
Seen as no1 has mentioned it, iam going to plug the forever war
The Forever War: Joe Haldeman. Excellent book, but goodluck finding it, it was written 30 years ago and most librarys dont carry it. I found my copy in perfect condition in a secondhand bookstore for $1. I would have paid upwards of $40 to get it.