I'm sure many of you DMs out there are tinkerers like myself. I do the same thing in my professional life to be honest. I can rarely leave good enough alone and I seem to always be tinkering with classes that I've taught for 10+ years just to see if there's a better way to do things. I suppose it should come as no surprise that I've tinkered around with most ideas for house rules at one point or the other. Shields Shall be Broken, Critical Hits & Fumbles, the d30 rule, you name it, I've pretty much tried it.
Shields Shall be Broken I found this one to be very flavorful, but it's just a bit too cumbersome really. In essence, this is a get-out-of-jail free card for your fighter types. Now, I'm all for making fighter types more attractive, but our group grew tired of it very quickly. I do think it's one of the best bennies you can throw to low level fighters, but what about orcs, hobgobs, and other mooks? Shouldn't they exploit the rule also? In the end, it started to become a joke in our groups and seems no different than situational giving your melee combatants additional hit points.
The d30 Rule I still like the hilarity of this one and could probably be talked into using it again sometime. The one thing that bugs me the most though is that occasionally, it makes a mockery of your Big Dramatic Chapter Ending Battle. Surely this could be fixed by giving your Big Bad Evil Guy d30 Immunity or the like, but to me, that seems a little inelegant. I mean, your players are going to want to save the roll 'til the absolutely most critical moment of the evening. No doubt they're going to feel a bit cheated when every Boss Monster happens to be wearing his Cloak of d30 Immunity. It's a fun rule, I'm sure others have found a work-around for the issues our groups had with it, but it just made for too many anti-climactic moments in our games so we stopped using it some time ago.
Critical Hits & Fumbles OK, so I get that EGG completely hated the notion of these, but to me, they're still fun and make combat more varied and exciting. They've been around since, oh, I don't know, the early 80s I guess, and I always enjoyed using them if and when you can find the sweet spot for using them in your game (that is to say, the implementation that makes combat more exciting without overwhelming the PCs). If my Google Fu is correct, it was Dragon Magazine Issue 39 that brought us that lovely Good Hits and Bad Misses article and that was the first time I used them (much to the consternation of my dubious players at the time). I modified it though so that we only used the chart on a natural 20 or a 1 just for simplicity (and still do). Initially, after much bloodshed and hilarity, it became apparent that allowing every scrubby kobold a chance at beheading the PCs is simply too much (or maybe not depending on what you're trying to achieve with your game).
I do agree that the 3.X solution is quite elegant (certainly one of the things that 3.X got right), but it adds more dice rolling than I really want in my Old School games. Over the years, I've tried the absolutely murderous Rolemaster Charts, took a shot at adapting the hysterically gory WFRP 1E criticals, the Paizo critical & fumble cards (which I quite like for d20 sorts of games), and now have arrived full circle back to the good ol' charts from Good Hits and Bad Misses. I think the sweet spot for old school play is simply saying this rule applies to all PCs, Named NPCs and Boss Monsters. I warn my players that most encounters, but certainly not all, will contain a Boss Monster, a leader type who won't always self-identify, but will usually become apparent that he has a tub-load of HPs and seems to be better at fighting than the other scrubs. Needless to say, this make something like a Boss Ghoul with 3 shots at dropping a 20 on you an enemy that even experienced characters will respect.
Death & Dismemberment I've tried a couple different versions of these charts and finally got around to making my own. It makes for a very gritty campaign as PCs and followers will lose limbs and the like as well as having very funny (or serious I guess if your group looks at it that way) death scenes. This does give low level guys a bit better odds at survival unless of course the bad guys are the carnivorous types that immediately begin chompin' on fallen PCs, provided of course that someone in the party survives the encounter to bind their wounds. When characters are bleeding out due to this rule, I allow anyone to apply first aid simply by moving to them (in lieu of attacking or casting a spell).
The one thing that bugged me about the other charts was that a guy would hit the ground and on some rare results, would simply spring back up with renewed energy to continue the fight. On most results though, the character would fall to the ground gravely wounded, their fate uncertain until someone could get to them to check out their condition. I decided that for my campaign, I didn't like the idea of a character jumping and getting right back into the fight, so I devised a series of modifiers for the roll and developed new benefit for those lucky enough to roll an 11 or 12. It works for my Gonzo Old School Setting of Moog, so try it out if you like the idea of the Oscar Scenes for your characters and their followers.
PDF download of Death & Dismemberment for Moog is HERE.
Binding Wounds After Combat I'll confess that I have no idea where I got this one. I know that some folks use a d3, but I like the d4 and I allow any character to do the wound binding (only once per combat in which you have taken damage and immediately afterwards). It's particularly useful at low level when many clerics may have little (if any, depending on which rule set you're use) healing and helps the party keep exploring rather than the old "hey, we're out of healing, guess it's time to head back to the pub for pints lads" paradigm that occurs otherwise. This rule is essential I think when playing in large groups or with kids or newbies. It also takes care of the situation, that I find to be all too familiar if I'm being honest, where no one wants to play the Cleric.
Saving Throw as an Indicator of Class-Related or Race-Related Skills, Knowledge, etc. Another one that I'm not really sure where it came from, but I use it in every old school game I run. In my games, characters are generally "adventurers". The ranger knows the stuff that rangers know. Thieves know the best place to pawn stolen goods and the like. If players want to add a bit of background by utilizing the secondary skills chart from the 1E DMG, that's fine by me. I usually play with the conceit that Magic Users and Elves know about ancient mysteries in much the way that Gandalf or Elrond would. I will typically use the Paralysis save unless I'm playing S&W White Box which has only 1 save (which I love, love, love). It's not perfect by any means and yes, dwarves and halflings in this sort of situation tend to benefit from their superior saves, but you can limit that by deciding that their breadth of knowledge isn't quite as extensive as other races. I certainly find it adequate at representing a workable set of skills without becoming overburdened by a full blown d20 set of skills.