I was a fan of Flat-Out Love so when I heard there was going to be a book about the sister of one of the main characters, who herself was quite the memorable character, I definitely wanted to see how she turned out. Overall, I really enjoyed Flat-Out Celeste. Not only do we get a sweet and cute romance, we get a "not-so-normal" girl who is trying to fit it, who slowly learns that it's okay to stand out. I loved that it was about so much more than the romance and Celeste's quirky personality was so entertaining, I really liked her character. 
 Celeste is anything but ordinary. She's a super smart girl, but she's definitely socially awkward and doesn't have any friends. Since she's about to graduate and starting a new chapter in her life, she really wants to take a step out of her comfort zone, discover if there's more to life than just studying, and taking chances. Some of the things she tried were pretty funny and I was surprised she was able to do a lot of them, considering it was so unlike her, but that's what I loved about it. 
 While on her path to self-discovery, she starts a friendship with Justin, a college student who initially contacted her as a liaison for his university, who was interested in Celeste attending their school. I loved their conversations. They definitely balanced each other out pretty well, Justin being very out-going, friendly, with a touch of hyperactivity - perfect for a rather reserved person like Celeste. Their interactions were so cute and innocent, it was fun watching them fall in love. 
 You also get to see a bit of Matt and Julie, the main characters from the first book, here, too. While I like the couple, how their ending plays out felt a bit forced to me. I loved their ending, don't get me wrong, but there wasn't any build-up to it that made me believe something like that could happen. There needed to be something more, for me at least. 
 Either way, I enjoyed Flat-Out Celeste. It was adorable awkward and super sweet. If you're looking for a quick, light romance with quirky characters, you'll definitely enjoy this one.