I tried it for FS9 years ago but abandoned it. Whilst its a huge improvement over the default ATC its still not perfect. The thing I disliked most is that you have to read everything word by word from a script that appears in an onscreen box. If you fail to read the script out verbatim then VoxATC asks you to 'Say Again' until you get it right. I've had to read out clearances 3 or 4 times in some instances! The other issue that I had with it is that the phraseologies are US and UK based, which bears little to no resemblance to the RTF that we use here in NZ (UK is close though).
If you want to get 'as real as it gets' - sign up for a VatSim id and have a go at talking online to a virtual Air Traffic Controller - or log in as an observer to hear the RTF chatter. There's plenty of posts here and in
www.vatnz.net to get you started.
I've just had a new baby arrive so simming is out for me for the forseeable future, but I can't wait to get back into online flying again as its very, very realistic. Having said that, if you don't want the pressure of going online and don't mind the limitations, then VoxATC is a vast improvement over using the ATC text box! Pressing the 'Push to talk' button and having your speech recognised is pretty nifty!
Hope this helps!