First of all, the characters are really fun. They're normal in so many ways, but they have these really cool powers and special abilities. They have pretty normal names, but say the strangest and funniest things. They develop and change and make mistakes and generally are quite well-written characters.
Second, there are so many things going on in this book that you simply have to keep reading. There is mystery: What happened to Will's parents? What about his ghostly mentor? Where exactly is the Other Side, and where did it come from? There is action: training their special abilities, running from bad guys, chasing bad guys, fighting bad guys. There is romance: Will crushes on one of his roommates, and it is pretty adorable. There is comedy: Nick is hilarious. That is all. Everything culminates in an all-out battle against The Other Side, which won't end up like you expect it to at all!
The only thing that would have made it better was the possibility of adding a little more exposition in the beginning, reminding readers where the Academy is, who Will's friends are, and who his enemies are. There is an entertaining Will-narrated recap of what happened at the end of the first book, but some readers might be confused through the first 5 chapters without that character-focused exposition.
Overall I really enjoyed Alliance, and I look forward to the next book in the series! Fans of The Maze Runner, I Am Number Four, the X-Men, and Lydia Kang's Control will definitely enjoy The Paladin Prophecy as well!