First things first, this will not be the "complete" system. I need more time to think about it and until code hits the debug step I don't want to be to attached to something that may have to change. Anyway as I mentioned previously I want my system to be somewhat like how BESM d20 does it. In its system not only do you roll to attack but also roll to defend so instead of a static defense you have a bonus to defense that you add to a d20 roll trying to beat the opponents d20 roll and their bonus to hit. Another quirk is that armor instead of adding to defense adds to DR. I do have a slight problem with how DR normally works but the DM for my BESM d20 campaign has an interesting fix that I think I will use.
The defense roll is a little to random for what I want though. Also one of the few ways to increase it is though Dexterity bonus. The Dex bonus though goes away if you catch them flatfooted and is reduced by heavy armor so it is easy to get around. My idea is that instead of a D20 what you normally roll will be a D10 plus 10 and when you are flatfooted you get to keep your defense bonus but have to use a D20 roll. This almost fits exactly what I want except that the lower limit is 11 and I would prefer 10 so for the roguelike, since I am not limited by physical dice I will probably either use 10 plus a random number from 0 to 10 or 9 plus a random number from 1 to 11. I don't think either way makes much difference in the end so whichever works better in code will probably be what is used.
As for armor as DR as far as I am concerned it makes more sense in the combat system I want. For the original D&D system where each combat round was a minute representing pitched battle it works because then the armor is counted as having blocked the attack a number of times in the defense. The problems with it for me come about when you get into the current understanding of such systems where a round of combat is a single attack or possibly a short series of attacks if your really good. In such a system yes adding to the AC could mean its helping defend the player by taking hits but when you also add your Dexterity it starts to lose meaning and become more of a number. When used as DR though it is clear in how armor works. The armor is taking a hit for you and the amount of damage it saves you from taking is right there in black and white. There is a problem with DR though.
DR as is means that beyond a certain point nothing but a few things can hurt you and anything that specializes in many weak attacks over one strong attack, no matter how many, could end up doing nothing to you. The fix that my DM uses is that if the attack would deal more then half your DR rounded up you still take a point of damage. This could represent many things in combat such as the tip of the tip of a dagger getting through a ring in your chain mail or any other similar thing. Low level enemies will still probably end up having most of their attacks completely ignored but someone at your level will still be able to hit you for damage. This feels right to me though I may tweak the final outcome like having it be two thirds instead of a half so that the game balances like I want it. After all I don't want to punish someone who boosts their DR to insane amounts but on the other hand I don't want to make it a cake walk for them.