Well, from what I've gathered from scanning quickly through these other posts, I've probably spent more time on it than many of these other people. The free game entertains you for a little, but once you start to grasp just how much more content is in the members version, you quickly want to upgrade. I did, and got a high leveled character (if I remember right, I stopped at 104) after about a year of on and off playing.
After all that, looking back, I can honestly say that my time as a free player was a lot more fun than the members' period, and I think I know why now. As soon as you gain something, as soon as you achieve a goal you set for yourself, you immediately desire something better. Obviously, this is normal in this sort of game, but for me, it killed the fun. The game became a never ending quest to get "the next better item", and there was never any chance to actually ENJOY what you just worked for. The economy of the game was pretty messed up as well, being entirely supported by the trade of rare and ultra expensive items. I quit when they ruined the last fun part of the game: the Wilderness. In a series of VERY stupid updates, they drained the last bit of enjoyment from the game and altered everything so much, it was nothing like the good ol' "fun" days I had had.
Long story short: It's legitimately fun for a few weeks as a free player before you've learned too much.