According to Google’s announcement, the app and the web interface have been given an overhaul in terms of design. In terms of features, Google says, “The first thing you’ll notice about the updated Google Voice apps is a cleaner, more intuitive design that keeps everything organized.”
“Your inbox now has separate tabs for text messages, calls and voicemails. Conversations stay in one continuous thread, so you can easily see all your messages from each of your contacts in one place. We’ve upgraded the messaging experience with support for group and photo MMS as well as in-notification replies. And we’re starting to introduce voicemail transcription for Spanish and will improve accuracy over time.”
Google also expects that moving forward they will be keeping its Voice service updated every now and then, as opposed to letting it lapse like they did before. The updates and changes are being rolled out today so you should be able to see the changes shortly.