I've played through DI & DIR a couple of times with each character. I found they're different enough to keep it interesting. I now have DIR with a character maxed out with all the best weapons so I can just go through the maps slaughtering zombies and accumulating cash (I usually get up to 700-800k before I get drunk and careless and killed). I was getting bored with this though so I picked up the L4D bundle. The games (DI & L4D) are remarkably similar in many aspects, but different enough, I guess. At first I liked how L4D1 was all guns all the time, but I do kind of miss the envenomed katana and other great melee weapons you can 'build' from assorted bits and bobs. Looking forward to L4D2 in March!
EDITED: 17 Feb 2016 16:28 by DSMITHHFX