I can't believe I've done it myself! Since ages I told everyone whose opening I read and contained too much back story, not to do it, to web it in, to introduce it slowly and bit by bit, but ignored my own advice.
The reason being is that I've never written a sequel. I'm sure I wouldn't have done it with a new book, but the sequel is a different animal entirely. I created a scene with four people talking to each other, and two people, who are absent, introduced in the first 400 words. Now that's what I call tight writing, tight, but wrong.
I had a feeling it might be too much information and back story crammed into the opening and got the confirmation from a friend I sent it to. Nothing I couldn't fix easily, but something that shows once again, as writers we need feedback, best in the early stages to avoid big rewrites.
Sequels need to be able to stand alone, so while back story is important, it shouldn't have the function of a teaser for the other books in a series. It's a challenge to connect the books without going too deep into what happened in the first one. But you need to introduce the characters to readers who start with the second book.
Since I'm experiencing this now for the first time, I take my hat off to every single author who's managed that effortlessly.
I'll also have the task to go deeper into some of the characters that played minor roles in the first book, plus I'll add some more characters, especially for the dark side. Keeping the balance between romantic comedy and paranormal will be a lot harder for the sequel, I want to keep the light tone of the first book, the wonderful intimate moments between Celia and Tom, but without repeating them.
Well, something positive came out of it: he liked the writing and the scene itself. Go, me! ;-)