And it is very easy to add your own hacks and optional rules. When we played we did a couple of things that made it a bit more involved but still left it streamlined:
-Gave Investigators 1 or 2 hobbies to supplement their occupation (e.g. we had a nurse who studied local history in her spare time, and a cop who liked to fish and sail) and let them roll the bonus occupation die when they did anything related to these. Which I think made the characters less one dimensional without giving too much power.
-Wrote up one paragraph biographies and required justification from character background if a technical skill wasn't covered by occupation or hobby to even get the "human capability" roll. To draw from some of the examples that came up: climbing a tree is something everyone can do, but lockpicking or tinkering with electrical wiring required justification to even make the basic roll. (The cop was able to justify lockpicking from a rough and tumble childhood in a gang and thus got his one die, but neither of them could justify the ability to tinker with a broken fuse box).
-Used the optional Harm rules from the official sources and mocked together...not really a combat system, more like an injury system. Bashing damage (falling, fisticuffs, etc) was done on the harm die as written. Lethal damage (knives, guns) afforded characters a coin toss; either they died instantly or rolled the harm die. Aggravated damage (magic, giant monsters, coup-de-grace, anything that should common-sense cause instant death) caused instant death. This allowed them to have consequences from clumsiness, still take on cultists albeit in high risk combat, and kept monsters terrifying and lethal.
-And lastly we did away with re-rolls, it just didn't seem to jive with the air of dire finality.
Currently we are brainstorming a way to make play more long term. Historically I have gravitated towards the drawn out CoC scenarios where you can take weeks to research tomes, spend stretches of temporary insanity in the hospital, make relatively sedate trips cross-country to consult experts, etc. all while the slowly looming horror grows and the stars move towards alignment. So to that end we are looking at working up some medical/psychiatric care rules, some injury/temporary insanity rules, and re-introducing the Cthulhu mythos skill sort of thing (that last one to be done with 'mythos points' which drive your insanity die ever higher; 6 at one time means you either need to head to an asylum or a cult ^_^).
All in all, it is a great system as written and fertile ground for houserules!