I'm GMing Delta Green once a month.
On the first Saturday of any given month I gather with a few people (currently down to 3 others, but there have been as many as 8 others at the table in bygone days) and we play out a modern day, conspiracy-theory heavy cross between X-files and Cthulhu Now using the D20 version of Call of Cthulhu.
I picked D20 in part because I wanted an action/adventure feel for the campaign, but mostly because I was using the whole Delta Green thing to challenge my assumptions.
Call of Cthulhu GMs tend to be reactionary sticks-in-the-mud who cleave to the BRP or Nothing mantra. BRP, or Basic Role Playing, is the system from which Call of Cthulhu is adapted and it is a simple-to-use game engine that lends itself to quick uptake.
A character has less than twenty attributes to take care of, most of them derived from the core attributes generated by rolling dice in the familiar RPG manner, and a list of skills he/she selects to reflect competences in various disciplines. The list can be a tad arbitrary depending on the published version you are using, and GMs are encouraged to use it as a springboard rather than a finite limit on what can and cannot be achieved by a character.
BRP advancement involves identifying the skills used "successfully" by characters and allowing attempts to increase these skills at an adventure's end.
D20 is a rather more complex affair, adding (some would say "larding") to the richness of the player character build-outs with experience-earned "feats" that give characters special abilities above and beyond the skills the system also offers. D20 also has the hated "levels" that are a legacy of the D&D RPG that started the ball rolling and which drive the BRP or Nothing Brigade to apoplexy.
Advancement in D20 involves the use of "Experience Points" that are collected until one has enough to "level up". Once a player increases a character's level, that character gets more hit points, gains increases in various bonuses (to attacks and various "saving throws" that grant reprieve from pitfalls, mental attacks and poisons to name but three) more feats and points towards the purchase of more skills and so forth.
I picked D20 and Delta Green five years ago as a way to open my mind to two things I'd always turned away from without really thinking about it. I didn't care for the incredibly detailed background of Delta Green, never really found that end-of-the-millennium paranoia to my taste to be honest, and had the standard BRP or Nothing GM's stance on Call of Cthulhu.
But I had the books, and the D20 book had some rather good ideas in it. Moreover, it made the whole business of players being able to access the ancient and maddening books of magical lore much more like the original first edition of the game. Later editions had strived to make the business of reading a magic book and being seduced by the lure of power something that took so long no player would ever consider doing it. One book famously takes over a year to read!
I had long held that the model for this nonsense was "obviously" derived from the story The Dunwich Horror, but that story is really detailing the process of Magical Research rather than a straight reading.
The BRP way of dealing with books is also intended to be a "between sessions downtime" thing, something I hadn't realized until I read John Tynes' way of doing things, which is not only an in-game affair but is more evocative and just all-round better in every way than the stilted and rather pedestrian BRP loss of sanity between sessions method.
A few games saw players being lured in and coming, inevitably, to bad ends for the best reasons and doing so from the most altruistic drives. It was wonderful, and the sense of wonder was back in the game. I was happy.
I also liked having the possibility of mass combat with modern weapons actually be manageable. I wanted to be able to model 50 debased inhabitants of Innsmouth chasing panicked investigators armed with Glocks through the streets at dead of night with the fog rolling in off the ocean.
BRP GMs scream another old mantra "If you are using combat you are doing something wrong" but that is an overly broad interpretation of the game's reality and contradicted by the content in the published scenarios and campaigns, just about all of which feature combat prominently.
There is a school of thought that the reason people don't fight in Call of Cthulhu is tha the combat system doesn't work very well. It is derived from a rather persnickety combat system intended to model hand-to-hand combat with edged weapons and shields, and really doesn't port well into a "scared academic with a pistol" scenario, let alone the "four ex-marines with advanced tactical training and mac-10s" scenario.
D20's combat system addresses those concerns by providing a robust combat system that can be played out on a grid (BRP Call of Cthulhu didn't even specify the speed character could move, making a mockery of the old joke about Call of Cthulhu player characters having higher "flee" rates than shooting skills - everyone moved at the speed of plot.)
It turned out that just about all the concerns BRP GMs were using as places to stand and dig in their levers were non-issues.
The hit points thing ("The PCs end-up being God-Like") is simply not true. The D20 rules have and always have had something called a Massive Damage rule, which is a level of damage inflicted at which a character must take a Fortitude Save - Difficulty Check 15 - which if failed is instant death. The monsters have the same rule, but the damage threshold is 50.
This means that you would have to inflict 50 points of damage in a single attack to stand any chance of killing a powerful thing from hell, but it would only have to cause ten points of damage to you - and almost forgone conclusion and one that had people dropping like flies until they learned to keep their distance from the nasties. Just like they do in BRP.
As for the levels, well, the players tend to be irretrievably mad or so fragile they'll go mad at the drop of a tentacle long before they become "Godlike". There are only so many things man was not meant to know you can look at before you are about as stable as a three legged cow.
And the game has become fun again. If you check out the forums you'll find them depressingly full of people claiming that their players "don't get" Call of Cthulhu and that they can't seem to scare up a game these days. The evidence is right there in front of these GMs - no-one enjoys the rather sterile experience of Call of Cthulhu as it has become. I also couldn't scare up a trad Call of Cthulhu game, but people were eagerly waiting each month for the Delta Green game. I had players who fell into the lure of Eldritch Power with predictable results. I had players gleefully treading the path to madness. All having fun doing so.
And that game has generated more deep immersion "buy in" than any other I've run. The sheer effort the players drove me to at times to provide them with challenging and interesting mysteries was exhausting. I've throttled back a bit, running some published scenarios rather than home-brewing them, because I couldn't sustain the mental effort any longer.
All from a setting and rules-set I had initially thought worthless.
