Never got going for me. I have seen various reports of player numbers dropping after the initial take up, but like Wildstar, I don't believe any official figures from the companies involved have been released yet.
I got to VR10, and gave up. After completing all the normal maps I got to looking for quests in Craglorn. I had two quest lines where I'd got almost to the end but the group had to quit, and it was far too much hassle to try to find people who had got to the same point, and I didn't want to slog all the way through from the start of them again. Getting any group together was a hassle. Another time I helped the group I was in fight through several tough bossess only to find I had got no benefit because I hadn't initiated the relevant quest. All I really had to aim for was VR12, but once I had got to it nothing would have changed except for no longer having the motivation provided by levelling up, so I gave up.
And although I went to Cyrodiil at least 6 times I never found a battle to join in with.