LabMUD was introduced to me by one of the staff. I had never played a MUD before, and had no real idea what I was in for. I was apparently in for a helpful, welcoming community all too eager to let a new player get steady on their feet, and an addictive and enthralling RP experience.
The MUD is in alpha, and it's still an enjoyable experience. It's well-made, and there's love and care in every corner of the code. (Also they made a newbie guide, which I'm very thankful for.)
I've never played a MUD before, but LabMUD changed that for good. I fully intend to branch out from here and play more MUDs on the FutureMUD engine and beyond. LabMUD has thoroughly hooked me, and I can't recommend it more.