I also agree the first series was more enjoyable than the second. So many odd plot devices and dumb twists in series 2! Hopefully they'll get back on track for series 3.
As for books that feel like they run along those lines, here are a few suggestions:
The Pursuit of Love by Nancy Mitford.
Goodbye to All That by Robert Graves. (His WWI memoir. Not available as an ebook in the USA as far as I can tell.)
Birdsong by Sebastian Faulks. (Also hard to find as an ebook in the USA.)
The Remains of the Day by Kazuo Ishiguro.
If you like poetry, I'd recommend
Wilfred Owen.