I think the nature of DOOM's uncomplicated engine makes it easy to port. You don't need special hardware to draw it's graphics, and there's not even a Z-buffer

I think the nature of DOOM's uncomplicated engine makes it easy to port. You don't need special hardware to draw it's graphics, and there's not even a Z-buffer to render on-screen. The folks at ID also make an effort to open-source a lot of their older code, which makes the process of porting DOOM fairly easy. That, and the game still rules. I'll find any excuse I can to get people excited about Quake again...