This is my second month with VM, heading into my third, and overall for the price, it's been really a positive experience for me.
The first month I had issues with 3G being properly enabled. I would guess the biggest issue with VM has been data capacity with the massive influx of new users hopping on the Optimus train (I being one of them).
Otherwise, like others have mentioned, if you're in a good area for Sprint, you should be golden. Services other than the early 3g hiccup for me has been pretty top notch and considering what we're paying, it's an amazing value in mobile phones.
I've had service from T-Mobile, Verizon, and Sprint, and I'd say it's easily comparable as any other in terms of services provided.
LeslieAnn is right, however. Customer service is... well... meh. But I've never received spectacular customer service from any of them really.
-K