I read the Wool omnibus last year.  The Shift series is technically a sequel, but it tells the story of what happened in the years prior to the events in the omnibus.

It was different than what I expected.  I thought First Shift was even better than the omnibus. Chapter 18 was a shock.  I never saw that coming!

I didn't like Second Shift as much, but it was still interesting, and I'm sure it's integral to the storyline.  I might change my mind once I've read the next book.

I decided to take a break from this series.  I'm currently reading Below Stairs by Margaret Powell.  I'm about 50% into it.

My current (short) TBR pile
* Hollow City- Ransom Riggs
* Third Shift: Pact- Hugh Howey
* Dust- Hugh Howey
* H.P. Lovecraft: The Complete Fiction- B&N Classics series