When it works (most of the time for most people) it's OK.
But VM's customer service is even worse than in previous years, so if things go wrong it's slow and unpleasant to deal with VM, and getting simple things fixed can take forever. New installations remain a source of lengthy delays for a few people (over a year in one case). Any intermittent connection fault will be very difficult to get taken seriously and fixed (how's my complaint coming along VM?).
If you're looking at Trustpilot reviews, then be aware that VM are actively inviting customers to leave reviews in situations where VM judge they'll get a positive marking - you can see those because they say "Invited" next to the individual star rating. Ignore all invited reviews, as it looks like they're mostly non-tech support interactions, and often simple upgrades that it would be difficult to screw up, even for VM (and there were over 30,000 invited interviews by VM in the past year). Then, bear in mind that the non-invited (organic) reviews exist because the reviewer was motivated to leave a review based on their experience, and that tends for all companies to result in being "overweight" in bad reviews. What's more important is to read the content of a few dozen reviews, see if you're picking up themes or recurrent issues, whether these are an acceptable level of problems, what they make you conclude.
Another way of looking at companies is to look at comparably sized companies, how many reviews from all sources do they get per month over recent months that had the lowest possible rating the reviewer could award? For VM, that's around 700 a month. EE only had 150 on that basis. Sky got about 130.
So are VM any good? I'll award them a solid "meh". In terms of what that means for you, it really depends on what your alternative options are.
