I have it. It's decent at best. For the most realism, you have to select a timeframe late at night for an airport that's not too busy. Otherwise, it will throw tons of traffic at you. It's unrealistic that a controller would have to work that many aircraft at once.
If it were set up so you were only working one sector of a TRACON it'd be great....and much more realistic. I don't have it set up for voice recognition, but a friend of mine does. I'll watch him using it sometimes and he'll often have to repeat clearances and you have to speak very clearly and slowly. So, for what it's made for when it comes to voice recognition it's good, but you'd never talk to aircraft that way in real life. But the fact that you actually can talk to aircraft is a good aspect.
If there was some way to just work part of a TRACONs airspace, it'd be great. But you have to use the lowest levels to be close to a traffic level that's realistic. VATSIM is probably your best bet. I haven't gotten into it yet, but a friend from the message board is moving here to Purdue and it looks like he'll have me hooked very soon.