The most recent book I almost finished but didn't was Thomas Pynchon's
Vineland. I'd read both
V and
Gravity's Rainbow twice (extraordinary books both) but
Vineland didn't grab me the way its two predecessors did.
I have another fat Pynchon tome waiting in the wings. I bought
The Mason-Dixon Line on a whim at a book launch where they had been serving white wine but I don't hold out much hope for it.
Pynchon is my favourite author, and I've read everything he has written.
Mason & Dixon is such a beautiful book. Full of some of Pynchon's best prose and descriptions. Read the first few pages and
savour it! If you like Gravity's Rainbow, it will hopefully resonate with you. Think of the description of the parabola of a thrown snowball as a great in-joke

My personal favourite Pynchon is
Against the Day. A 1000-page monster of ideas, conscience, humour and changing styles. His magnum opus, imo. There is a great web resource for read-alongs,
http://chumpsofchoice.blogspot.co.uk/2006/12/now-single-up-all-lines.htmlVineland, and it's cousins
Inherent Vice and
Bleeding Edge, are less satisfying to me, but still contain enough
Pynchon to elevate them above most other authors' works.