When D&D 3E came out, every group playing it quickly accumulated numerous house rules. A few of those were eliminated or replaced by the (necessary or not) 3.5 revision. And the circle began anew.
After third edition was replaced by its makers, in their infinite wisdom, further progress went in many directions. The current favorite seems to be Pathfinder, which (to me) is more a house-ruled version of 3.5, with more expansions than fixes, albeit heavily playtested. It still doesn't fix a lot of the problematic points, and at some levels it actually made 'em worse (even more home-brewed magic items, archers as immobile as fighters, to pay for their new-found efficiency.) Then there's Fantasy Craft, which basically remodels the whole system. While being rather scrumptious, it's not really a drop-in replacement for existing 3E products, and requires heavy investment from both players and the DM.
Trailblazer takes a rather surgical approach compared to those other offerings. And as any good surgery, it starts with a good deal of diagnosis, dissecting the existing mechanics and analyzing the delicate "game balance". Class features and challenge ratings are broken down into mathematical variables and compared to each other. It's not a hugely complicated affair that could only be solved by supercomputers crunching along for eons, but it's a lot more than I've seen from other authors and publishers.
Based on this "spine" of the system, as the authors call it, we get some precision rule replacement. There's no huge remodeling, so almost any rule can be integrated into your preferred 3E variant without many problems. They're not trying for a different experience, they're not trying to completely change the fundamentals of the existing design. What we get is some fixes for the usual suspects: Fighters being bored, mid- to high-level rogues being ineffective, casters who would like to multi-class but don't want to fall behind too much, dependence on the "big six" magic items, overshadowing more interesting ones and the 15 minute work-day, my personal least favored aspect of the game since it came in a small white box.
Coming back to the medical analogy: In a typical House M.D. episode you get at least two dangerously wrong diagnoses, before the right cure is found. Trailblazer comes pretty close to being that for 3E…