So, here's the thing. When you read a book after having first seen the adaptation, you come into it with expectations. Lately I haven't found an adapted book that's disappointed me, but there's always that worry that you won't like the source material as much, and maybe it'll ruin the adaptation you loved -- or perhaps, the book will be so much better that you'll never be able to watch the adaptation again without noticing everything it did wrong. 

Good Omens is none of those. I'd say it's just as good as the television series, which I absolutely adore. Of course, the show has certain things that the book doesn't and vice versa, but considering that they're different mediums, and it made sense for some things to be in one version and not the other, it doesn't hinder your experience of either. 

Personally, I suggest watching the show first. I think I had an easier time of understanding it (especially how to imagine characters or places) because I read the book after I saw the show, so that's the order I'd recommend. Show, then book, in my opinion. I don't think you can go wrong either way, though. 

A side note: the show and the book are, for the most part, pretty word-to-word. I really like that, because it's always fun to spot the lines that have been directly taken from the book, like little Easter eggs. The thing with Good Omens is that I feel like the book scenes were basically perfect as they were, so altering them a lot, and only using a few things directly from them, wouldn't have felt right. 

Another side note: you gain a better appreciation of the show, and the casting especially, after you read the book. Seriously. Just thinking about anyone else as Crowley and Aziraphale feels wrong. 

Even before I finally got around to watching the show, I'd heard it was good, and I'd heard that the book was really funny. I have a hard time believing people when they say things like that, because humor is subjective and I tend not to find things funny that other people I know do, so I tried to lower my expectations. 

But now that I've read it, I can safely say it really is hilarious. I love humor in books, but getting me to physically react to it is hard. And I found myself smiling all the time while I was reading it, because the humor is just as funny even if you know what's coming. So, kudos for being the comedy it promised. 

There are so many things I love about this book. The characters, the parallels, the way it talked about good vs evil and humanity and destiny and all sorts of themes that I find really fascinating. The humor, obviously. The relationships (Aziraphale and Crowley most of all, they're so precious), the footnotes, the way the different storylines came together. 

You can't go wrong with Good Omens. It's the kind of book that, the minute you finish it, you desperately want to re-read, and you have to hold yourself back because you have a huge TBR and you should probably get through it first. It's probably my all-time favourite apocalypse story now. I'm already excited to read it again; I just know I'll find even more things to love.

REREAD EDIT: I'm always worried, when I reread a book, that I won't like it as much as I did the first time. I'm always thinking, will reading it again ruin it for me? Did I only like this book because I liked the adaptation, and not because it was particularly good? I can safely say now that, in fact, I think I loved Good Omens more now than I did at first. The first time I read it, I was still caught up on the show, and so I viewed it through that very specific lens that comes with adoring the adaptation and wanting to catch all the similarities and things it gets right. Now, however, I was able to fully appreciate the book on its own, as a separate entity. And oh, it's still just as good, if not better. I actually caught quite a lot of little jokes and things that I'm sure I missed the first time around, which was a nice surprise! This is such a rereadable book. Really, I don't think I'll ever have enough of it. So even if you've already read it, I highly recommend reading it again.