TorilMUD is one of the biggest, deepest MUDs I've played. It doesn't take long to pick up the basics such as leveling. It's the exploring, questing, and end-game zoning which takes up the vast majority of time and effort. The zones are fantastically detailed, and with so many to choose from, there's always a new place to explore and new mobs to check for quests.

The world itself fits into the Forgotten Realms after the Time of Troubles but before events like 4th Edition. With 300+ zones, I'm surprised there's hardly any deviation from valid theme in the game. It prevents a very serious, professional in-character view of the entire world.

There are some excellent player resources like a world map and equipment database. Information itself is a precious commodity, since there are so many difficult to obtain yet very powerful items and spells hidden behind vague quest info. Even a remort from Necromancer to Lich. The people in the game are generally happy to help even so.

There isn't much roleplaying, as it's primarily a hack-n-slash game with gathering more equipment as the primary objective, aside from beating the actual challenge of it. Rogues are especially valued as the class which provides the most flexibility to deal with encounters and problem situations, like taking out a healing, tracking dracolich or recovering a corpse from deep within a fogged grid of giants.

I've honed my MUD skills here far more than any other game, and it's made me a better player in other situations. TorilMUD is near the top of the challenge / reward hierarchy, and with 11 years of their no-pwipe policy still going strong, I can be assured that my rewards will remain as long as I want.

In general, it's a great place to smite baddies and quest for adventure.