I see this as definitely a good thing. Twitch has had many problems over the years and pretty much all of it down to money. They aren't a big company, their services exploded and they've been struggling since, it's why there's now those big delays on streams when there used to not be and why there's been no real big improvements in recent time. The sheer effort of
maintaining the service is taking up most of Twitch team's resources.
Best case scenario, Google lets Twitch function as they always have done with some extra funding, and that also seems to be the most likely scenario, Google are putting stock in the Twitch team rather than forcing them out and taking over. The streaming functions of Twitch will improve as servers are upgraded, and Google will hopefully let Twitch in on some Youtube tech in order to improve their horrible VOD service. I'd love some integration with Twitch and Youtube too, having an auto-VOD upload to your Youtube channel or something akin to that, but I think that's a pipe-dream. Better VODs, however, I don't think is and is something I think we will see.
As for people's worries about copyright things, well, it was only a matter of time to be fair. We very much live in a world of entitlement, "It's always been this way so it always should be!" type opinions being very common. Twitch isn't above the law and have been getting pressured about this stuff for a while I'd assume, and so Google will likely pile some (hopefully better than the first attempt) anti-copyright tech into Twitch to sort all the copyrighted music use. As long as they actually do it well, I don't see a problem with that really.
And as for Google+ integration, I'm not sure they'll actually do it. They could link accounts, which seems likely, but Twitch's chat interface is just a heavily modified IRC and so unless they completely re-do the chat from scratch or do some very odd interface loopholes and DB links then they can't just start using Google+ accounts. I wouldn't mind a chat re-work to be fair, but as long as we keep all the smilies.
Twitch wouldn't be twitch without
So, initial thoughts, good. I hope Google don't disappoint!