Reliability and service depends on the infrastructure in your area. In Edinburgh we've had an extensive, well maintained cable network since the late 80's. It's been managed and upgraded down the years by the various entities that have owned it, and it's been Virgin since the early 2000's IIRC
Service here is more or less impeccable. You get over and above the bandwidth you pay for, and outages are more or less a 'once in a blue moon' phenomenon, like once per calendar year or so. My biggest gripe with them is their CS can be awkward to deal with, and their webmail doesn't filter out nearly enough obvious spam, but apart from that they are rock-solid reliable and I have no issues.
The problem is, if you ask for opinions on Virgin, you are going to get a gamut of varying answers, because they serve the entire UK and in some parts of it the infrastructure just isn't there, so people living there will contend their service is garbage and advise you to avoid them like the plague, whereas where I am the service is faultless and I couldn't recommend any of the alternatives.
Be very specific about what you choose to listen to. If you are in London (for arguments sake), I wouldn't pay any attention to what someone in Newcastle says about them, because you are not buying the same product as someone at the other end of England.