All of the campaigns I have DMed have taken place in homebrewed worlds... inspired by everything from published adventures and settings to books and movies. In almost every case, my last campaign has always been my favorite. In other words... as both myself and my players get better and better at the style of game we play, the campaigns naturally become more and more enjoyable.
My current game, which I've titled "Ghosts of Indigo Marsh," has been an absolute blast. It has certainly been the most realized world I've created, and, likewise, the players have rolled up some truly interesting and engaging personalities. Essentially, the campaign focuses around a haunted swamp that was once home to the infamous Arcane's End, a prison specifically designed for nefarious wizards. In addition, the mysterious and powerful Westenra family has recently taken an uncommon interest in the ghostly denizens of Indigo Marsh, and it is up to the PCs to solve all of the riddles.
Here's the introduction that I read to the players at the start of the campaign. I typically introduce the main theme of the campaign and then begin to develop the physical atmosphere.
Legends... childish stories that take your mind to far away places with far away peoples. They are meant to excite, to fear, to mesmerize. However, if you allow yourself to walk that line between fantasy and reality, you may find that some legends die hard. You may find that others never die at all. You may find yourself in the haunted wastes of Indigo Marsh.
The sun turns red in the western sky, and purple shadows begin to fall on the swaying reeds. The namesake of Indigo Marsh reveals itself in its natural beauty. However, you know that the night will soon fall and that the colors will become memory. The salty vapors sting your nose again and rudely jolt you from your peaceful moment. The muddy sludge of the road sinks into your boots with each step, and the buzz of a hundred cranky flies fills your ears. You feel as if you are swimming, not walking, through the thick summer air. At least it isn't raining...