I'm a System Matters guy. I have always despised GURPS on principal, ever since I played GURPS Discworld—the laziest cash-in product I've ever had the misfortune of owning... or so I thought. I felt immense pressure when running it to be as clever as Terry Pratchett, something that was patently impossible. Our GURPS Discworld game was brief, and fraught with anxiety on my end. Looking back on it, I think my failures with Discworld stemmed more from my own hero-worship than anything else.
System Matters... but maybe GURPS can succeed at its goal of modularity in such a way as to not be one all-encompassing system, but rather every system to every one. A novel and, mayhaps, dangerous proposition. But I'm willing to give it another try, mostly because no other system does what I want (need?) right now.
I love systems. I love the way they interact distinctly with the worlds they simulate. Rules designed to model specific in-world truths are the best kind of rules, to my mind. I don't like "general" rules because they tend to lack the flavor and intimacy with the setting that more tailored rules provide. The clothing metaphor can be extended: rules taken off the shelf for simulating just any kind of game are baggy and don't fit well where they need to. Evidence of a well-fit system: Seventh Sea. Evidence of a poorly fit system: trying to play a modern game with AD&D.
Now, it occurred to me that I normally modify AD&D (or any rule system) heavily to fit with whatever setting I'm running if it isn't the standard out-of-the-box setting for that system. Hell, even the actual printed AD&D settings do this. There's no reason to simulate the effects of blazing desert heat on metal armor in standard AD&D, nor to consider the difficulties of alignment in a world where you might be determining who lives or dies based on water rationing. Yet, Dark Sun adds those things in to the system because they expand it.
Taking this as a jumping off point... it seems that is what GURPS does all the time. Every GURPS book is modular, all the GURPS books could conceivably be used together, and the steps to making them align are the same as if you were making a custom AD&D setting. Sure, there's no perfect combination of GURPS rules out there for whatever thing you're dreaming of. But you can build the Frankenstein monster that you're after.
Now, a caveat here is that this requires a large number of different GURPS books to bash together the appropriate rules for a complicated setting. In the world of purchasing RPG products, this makes perfect sense. Steve Jackson needs some way to keep you coming back to buy his game books. And that is really too bad for the consumer. I don't want to have to own somewhere around 20-30 books in order to create the setting I'm dreaming up. Of course, you can always make rules up for yourself, but the more complicated the core system the more dangerous that is. I feel comfortable eyeballing new AD&D rules all the time because AD&D is fairly simple at its heart. I hope that in time I'll feel the same with GURPS. Right now, it isn't so.
Of course, this limitation is much less of a problem if you don't need physical copies of every book.
Anyway, I've yet to play an extended GURPS game that lasted for longer than a handful of sessions... but I'm excited to give it a try.