I'd say if you are a casual talker, who does not rely on your cell for business conversations it may be worth a look. I'm a Sprint user, and when my wife's company mandated a move of her company's employees to Verizon she moved over and I put her on Google Voice because she could manage texts/voicemails so well from her desktop. The move was painful for her to say the least, since GV did not become her native dialer and she had to dial every call from w/in the GV app for the phone to broadcast her GV number in Caller ID (v/s her native number). Additionally (she's on iOS) the GV mobile app was pretty delicate, requiring frequent sign in/sign out and reinstalls. Lastly, while sms worked (for the most part) great - there is/was no MMS. All MMS (pics) are/were delivered to gmail. So, pretty clumsy to say the least. If you're super tech savvy and enjoy tinkering - no big deal, you get used to it....
Today, as you probably know, Google is converging GV functionality into Google+ Hangouts. A curtain call on GV is imminent. On my Android (Sprint), I've moved on to Hangouts, which on Android also offers a Dialer applet as well. Since I've been a power user of GV, and subsequently Hangouts - this convergence has been a labor of love. Hangouts VOIP calls continue to get better, but the integration is still half baked. As an example, when I want to make calls, I can't easily access my Google Contacts from Hangouts - some show up, some don't. Doesn't seem to be a rhyme or reason since very frequently used contacts don't show in Hangouts when I search - so that sends me back to my contacts searching for a number - again very clumsy. Other things I'd mention - if you've grown accustomed to being on the run and having to join concalls forget about dialing pauses/waits in a dialing string that you may be enjoying now, you have to manually dial passcodes and #'s to join calls. Again clumsy.
Things will continue to slowwwwly, incrementally get better, but as I've seen over the past number of years it does not seem to be a priority for Google. The good news is It's Free, and to that end it's hard to criticize something that's free. The bad news is that if you are going to rely on Google's offering (GV / Hangouts) as your absolute telcom backbone - have a thick skin.