Desert Bus is notoriously one of the most boring games of all time, and that, I suppose, is what's so good about it. Richard Cobbett named it in his article about the 11 most boring sims on PC, and it definitely belongs there: it's an eight hour drive through featureless virtual desert. Nothing happens and it sucks. That's what's so good about it.
Revenant Bus is a bit different. It's basically the Desert Bus experience brought to Doom 2, but with one major twist: a revenant spawns in the back of the bus every seven seconds. Given the lack of weapons (you have to punch the revenants to death) and the 24 hour duration of the bus trip (you need to go back for your wallet), that's a very monotonous bus trip indeed. But at least there's punching involved.
It's the work of .wad creator Revenant100, who seems to really love revenants. They're also responsible for 100,000 Revenants, Infinite Revenants, and The Revenant Problem. They're verily the arch-innovator when it comes to revenant-themed wads, in other words.
Here's a video of the .wad in action. You can grab it via this thread on Doomworld.