Here's a simple thing: I want to SMS a friend. I type in their name in my Hangouts OSX app. It brings up their GTalk interface. No. I want to SMS. In iOS texting or Android texting, all I need to do is search the name (obviously) to call/SMS. In Hangouts I need to know the person's number, so what I do is open the Google Voice app (which is deprecated), search their name, copy/paste their number into Hangouts, and SMS them. Ridiculous.
EDIT: Also, the OSX Hangouts app crashes about every 2 hours with no error message. This is a "known issue" of varying types on Google's site, but customer service with them, well, you know how that is.