In short: Though Pandemonium by Lauren Oliver is a much different book than its predecessor, the change in tone is a welcome one. 
 I was a bit apprehensive about reading Pandemonium because I loved Delirium so much and from all accounts Pandemonium was going to be very different book. A new locality, new friends, a new boy, and a new Lena. I didn't want change if it meant doing away with all the things that I adored about Delirium. Why fix it if it ain't broke? I think it's because of my doubt that it took me a while to become fully immersed in Pandemonium. Thankfully, Lauren Oliver's charm worked on me as it always does and it wasn't too long before I found myself appreciating the change in tone. 
 I remain astounded at Lauren Oliver's writing ability and talent in character development. To have such a drastic change in the story, a huge development in Lena's character, and a completely new love interest and have all of this be actually believable - now, that takes talent. I like the new Lena no more or less than the old Lena from Delirium, but I wholeheartedly appreciated seeing such growth and maturity in her character, rather than have her remain static for the entire series. Same goes with the new love interest, Julian - I was prepared to be offended at the introduction of this love triangle, but was quickly won over by him. It is a true love triangle for me because I honestly couldn't say which boy I like best for Lena. 
 Unfortunately however, I found that I wasn't held quite as captivated with Pandemonium as I was with Delirium, though the reason why is unknown to me. It's surprising that I would feel that way because in a way, Pandemonium was faster paced than Delirium. Pandemonium certainly had a few surprising twists that were quite interesting, and yet I found my attention drifting a bit more than I would have liked. For me, Pandemonium seemed to lack a lot of the magic of Delirium. I did still love Pandemonium, of course - by this point, I can't imagine not liking a Lauren Oliver book. I will be anxiously awaiting the third and final book in the trilogy, Requiem, to be published March 2013.