Read through the various forum topics (in particular 'Quick Start' and 'Managing Your Account - Cable') and you will get an idea of the problem issues that are being reported by customers at present. You can compare with what you have experienced in the past and judge how/if anything has changed.
Needless to say the forum mainly generates topics when problems arise with VM rather than being a place where happy customers come to heap praise on VM!
If you are switching back to VM though, a general piece of advice would be to keep your EE service running while you get VM installed and overlap the two for a short time if that is feasible and affordable for you. New installations is an area where VM often falls flat on its face (particularly if you need a cable installing) due to the way VM has outsourced the installation work.
If you keep your EE connection going until your VM service is up and running you will at least avoid being cut off with no services if an issue or delay crops up with getting VM installed.