I've been using the new Hangouts now since it got updated and I'm just now noticing a couple little things.
First, I kinda don't like when you tap to compose a new message how it gives you all the options (New SMS, New Conversation, etc). I get it, I understand why...but I just don't like it since all I personally use Hangouts for is the text app.
Second, in regards to texting...I was trying to compose a group text to some friends the other day. I was going to include my girlfriend on the group text but it only let me select one of her numbers that has no texting associated with it (her office number). I couldn't figure out how to make it switch over to her mobile number, even though I have a running text history with her mobile number already within Hangouts. That just doesn't make sense. I ended up copying and pasting the text that I sent to everyone else into a message just to her.
And lastly...unless I'm missing something, there doesn't seem to be a way to add text to a picture message that gets sent. Used to be able to do that but now that does not seem to be the case.