With Deathlands, yes, you can pretty much pick them up and read them in any order as there is very little (or, more often, no) book-to-book continuity.  This was less true in the first two dozen books or so when there were several characters coming and going from the plot line, but it has been probably a decade now since there were any significant character changes.  Well, there was the point a few years ago that Dean (Ryan's son) left the series, but I don't think that has been mentioned at all in the last dozen books either.  In any case, the books are specifically designed to be easy to pick up and read with little or no back story.

If you go to The Books section of this website you can see reviews and average ratings for each book, to see which ones to pick up or avoid.  There are definitely more than a few stinkers in the series, but there have also been quite a few bright spots.  Good luck!