Richard Strauss' Four Last Songs

I do not listen to vocal music very much, but for some reason, I found a need to listen to Strauss' Four Last Songs.  I have Elisabeth Schwarzkopf's famous EMI recording with George Szell, but the one I pulled out was Lucia Popp's EMI recording with Klaus Tennstedt.  Popp's last recording was Strauss' Four Last Songs (a newer Sony recording).  She died of cancer when only in her 50's. 

I remember hearing Rick Philips featuring the Four Last Songs on a discussing in his much missed, Sound Advice radio show on CBC Radio 2 (Saturdays).  I really love the 3rd song the most - Beim Schlafengehen (Going to sleep).