If your a free member, after like level 40 you'd probably completed all the quests. However, if your a member they regularly add quests, and there's a lot more monsters/places to explore.
I played it a few years ago, but then stopped. It got boring after a while, especially on the free account. A friend of my mine had a members account so I went to his house and tried it out. The game was better as a member, but even then I had played the game too much before, and didn't feel like playing again.
It's fun if you have a good PKer

The wilderness was my favorite part, but also it got me ticked off a few times since I lost some good items there due to lag or carelessness (didn't heal quick enough etc.)