Maybe this makes me shallow, but whether or not I find a main character "likeable" makes a huge difference in my enjoyment level. Love Hacked is a prime example. I have read the two previous books in Penny Reid's Knitting in the City series, and enjoyed Reid's humor and writing style, and liked the stories reasonably well, but rated both books only three stars because I found the main characters so unpleasant. Elizabeth (Friends Without Benefits) I found to be so toxic I couldn't see what the hero saw in her. Janie (Neanderthal Meets Human) was better, but still hard to connect with in that she's very rigid in her world view in a way that I am not. I warmed up to Janie's love, Quinn, but it took awhile, because at first blush he's a typical icy, reserved alpha male.
By contrast, I really, really liked both Sandra and Alex in Love Hacked. Sandra is funny, smart, and relatable, and Alex is one of the best contemporary heroes I've come across in months: he has a heartbreaking backstory, but it hasn't broken him, and he is honest and emotionally forthright (in contrast to alpha men like Quinn, who don't like to talk about their feelings or even acknowledge that they have any). -And the fact that I liked both characters so much made Love Hacked an almost five star read: everything I liked about Penny Reid's writing combined with a couple whose happiness I could invest in (because if I don't like a character, how am I supposed to give a damn about their HEA?).
I found the premise of this story really fascinating, too: more so than plain-jane-meets-billionaire (Neanderthal) or celebrity-pining-for-the-one-that-got-away (Friends). Sandra is a therapist who has spent two years trying to find Mr. Right, but no matter how normal they seem, they can't help but open up to her Magical-Therapist-Vibe and they always wind up crying before the first course. Alex is the waiter who has watched her reduce men to tears every Friday night for two years… but he's so much more than a waiter. Alex has a Tortured Past, but unlike all the other guys Sandra meets, he's not interested in letting her put on her Therapist Hat and poke around in his psyche. This means that Alex is the one guy that Sandra can't figure out, which makes him endlessly fascinating--but also scary.