IIRC the level (tier) cap was 25. The number of experience points required doubled every tier up until I think 15th, and then went up more steadily. Somewhere along the line, an approval system was put in place to advance to 15th, and later, advance to 20th. Deaths could be weeks of playtime in experience (let alone gold!) lost, double deaths even more so.
I remember we had a ton of discussions about how to keep people from getting too powerful, while still allowing people to “hunt” to their heart’s content. I think the approval system ended up getting pretty political and generally unfair to those who didn’t have GM connections, played at weird times so didn’t RP much, etc.
So how to keep people from getting too powerful? How do we keep people from getting bored/frustrated by a small player base? How do we keep people with different motivations coming back for years? These seem like general problems with muds.