It is actually a really, really good MMO, and they did quite well with the Elder Scrolls aspect. However, it did have its downfalls like any typical MMO launch that hurt its potential in securing a solid amount of subscribers. That isn't to say it doesn't have a stable playerbase, quite the opposite, but its potential was never truly succeeded after launch.
I will say though that the developers are still very passionate about the game, continually updating it with a vast amount of content and more to come. They are adding in stealing from anything or anyone, a guard system, more raids and more areas of Tamriel to explore. The timed trial dungeons/raids are also pretty cool, and are probably the best PvE content I've ever done.
Elder Scrolls Online going free-to-play won't be a bad thing, they'll just sell small things like costumes and the fabled horse armour. I would prefer them to take the Guild Wars 2 route as that would be a far better option, they still get box money and can supplement the whales of gaming with the extra DLC options.