And I'm not even talking about things like online-status 'missing' (it's a design decision on their end), but more the general experience of using hangouts.
As far as I can tell you're still not able to mute the new message sound, without turning off notifications all together (hangouts in Gmail). Chatter picking up in a hangout and you want to mute it for a while? Again, not possible. Turn off all notifications for that hangout and chances are you'll completely forget you were ever part of that conversation (snoozing notifications hangouts-wide makes sure you miss all other personal messages sent to you as well).
Uploading a photo on a slow network is a pretty terrible experience: it'll start telling you the upload has failed and it's retrying (no progress to be seen anywhere). If you delete the message and try again, you'll probably end up with two of the same messages in your conversation, because often it doesn't appear to correctly 'receive' your deletion request either.
When you've received a photo that you need to save to your gallery (maybe you want to zoom-in a little, or share it with someone else?), be prepared to hit that save button for a while until you finally get a confirmation that the photo has actually been saved.
Stuff like this is not a problem when it's your first release, but 4 months on you'd expect a company like Google to be able to iron out quirks like these. But no, we get extra emoji as one of the few updates to the hangouts platform.
[edit: spelling]