I'm trying to stay open-minded, but so far I really dislike this product. I hope gtalk stays open.
I think the Chrome app is an excellent cross platform solution (written once, easily maintainable). As for the protocol I don't think it is practical or even possible to built this sort of all encompassing communications platform on top of XMPP (see the competition).
I do hope there will be a Hangouts API.
I'll cross my fingers for a Hangouts API that allows me to write a standalone client. However, if chatting through a semi-broken browser extension (or memory intensive gmail tab) are my only options, then I guess the service isn't for me. I think the reason I'm annoyed is that I have a lot of important contacts on gtalk, so migrating away will be a challenge.
I know change is inevitable, that the service is free, and that they want to offer a better product. Perhaps my use cases are just too expensive to support in the long run.