DR JRand - Seriously...
It's about Life. Good and Evil. Family. From Creation through the Ice Age, The Deluge and the End(?) of the World. Admittedly, it's a lot of stuff to cover in three acts, but Wilder does it and in a very compact and unique way. Even the breaking of the fourth wall, which is more or less commonplace nowadays, still seems fresh and startling at times. -To me at least.
When was the last time you read the play? Wilder made some tweaks - very small ones - to the play throughout the years, but at one point and time, there were actually two different versions in print at the same time. Again, the tweaks were small with the most notable alteration in the Henry's breakdown in the third act), but I think they do make a difference in the end.
It's also one of those plays that plays better than it reads. Did you ever catch the Old Globe Production that Jack O'Brien directed when it was on PBS' "American Playhouse"? That's how I was introduced to the play, and I was so happy when it finally was made available on VHS (and DVD) as part of the Broadway Archive series. There are some fanciful moments here and there, and even some slight liberties taken with Wilder's text, but the play is there in spades, and it communicates Wilder's message quite effectively.