You've read a story like this, and it's been done better. Guy secretly likes the girl and she starts to warm up to him. If you've never read anything like that before you might like this, but it's been done to death and much better than done here.
It's filled with stereotypes and offers almost nothing unique. The writing itself isn't bad exactly, but it's not what I'd call good either. Then the characters, for what felt like most of the book, aren't being particularly nice to each other and are generally inconsistent and I couldn't stand how the girl was basically the guy's mom which is all too real since the MC is literally 15 years old. I was hoping something would change, that they'd start to have heartfelt moments, but they barely connect at all through this first book. And yes, that's why the title is about her being an angel, it's because she acts like the MCs mom, complete with nagging included. Honestly, that kinda grosses me out.
I wish I had more to critique than that but that's the whole first book. I have no idea why this is rated an 8 on MAL at the time of writing this.
Needless to say, I will not be reading the next entry.