The writing has been on the wall for Picasa for a long time. Google hasn't put any meaningful effort into the desktop photo manager or the website in years. Ever since Google+ arrived, Google has been cautious to even mention the name Picasa in any context.
The fact that Google+ Photos
uses the Picasa Web backend, or rather, that both services use the same technology, only made it clearer that Picasa was dead.
And now, you can call it official, visitors to the Picasa Web Albums site are automatically redirected to Google+ Photos, as the Google Operating System blog found
For now, you have the option of still using Picasa Web Albums, you get a link to go back from the Google+ Photos website when you are first redirected.
But it's quite clear that Google is "strongly" recommending that you start using the Google+ Photos interface.
While there are a few Picasa Web Albums features still missing from Google+ Photos and a few that will probably never be included, Google+ does have some advantages, and for viewing and sharing photos it's probably the better option already.