Pros Talk with a group of people.
Cons No presence info. Have to scroll to see who is available.
Summary They replaced Talk without providing any presence information. Talk shows people who are available on the top and you know, *before* you start chatting that they are available. If I had to wait for a response to know that, I can send an email or an SMS. This is not a replacement for IM. I have to scroll through a long list to discover who is available based on a barely distinguishable enabled/disabled icon.
Worse, once you install this, no one else can know whether you are available or not on their app. So even if you didn't install Hangout and were still using Talk, you are affected.
They need to allow installing Talk and Hangout work side by side until they work out the kinks. This is an alpha release that is taking away valuable features from an app that's been retired.
Sheer Hubris. Did this overnight with Google News and Contacts in Google Now. Backed out of both after an uprising. Google News is now excellent. Best of both world because I can customize it to use a two column layout. Contacts in Google Voice is just so messed up. Having to toggle between two web apps with a clunky Contacts app. Did the same thing with Gmail, but at least allowed you to preview it for many months before switching over.