Anarchy Online. It has a vast spectrum for what you'd call "success". It's 63 or so skills with very few profession/breed/level locks, it's also an end of life MMO that has a mostly veteran playerbase and a ruthless economy. Meaning, you can either get along with people and thrive or take a poke at it like a helpless noob and probably hate every minute of it. I love it's freedom, and the ability to twink characters is nearly endless compared to other games. However, without help, you're likely going to drown. I've played on and off since like 2006 or 2008 and I still feel like I have a lot to learn.
Perhaps that's why I like it so much. It's too big for me to "conquer" like most games and I do genuinely enjoy the long, complex challenge.
The community is generally extremely helpful though. Got handed more money than I'd need for months my first day back, for example.