What's the greatest book ever written and what makes it great? 

I don't know. Might be many contenders. For me, the ones I've loved are either ones that made me think lots or ones whose plots were so well crafted that the artistry got to me. 

Really hard to find series that you can just dig into though. The last I loved is maybe open, which I read incessantly. But really want to find more that are meaty.