I barely even put my toe in the ocean of Westlake's prose before he passed on New Year's Eve. I have only read one of his books, Somebody Owes Me Money (Hard Case Crime). My review is here. Needless to say, I thoroughly enjoyed the book and look forward to reading more.
There are better outlets with many more links. The Rap Sheet has some good links as well as Sarah Weinman.
Suffice it to say, we've lost a giant. And a standard by which all crime fiction must be measured. I think we're all in Westlake's debt.