There is a very strong meme out there that GURPS is for gearheads. Number crunchers. Detail freaks. Rules-happy crunch-fans.
I don't think this is true.
I do think GURPS provides some very solid support for gearheads.
But equally, GURPS provides very solid support for dramatic based gaming, and for rules-medium gaming, too. It's an easy enough system that people who really just want a "basic set" solution and want to fudge the details can have that, too, while still benefiting from the thought that went into the system.
First off, what's a gearhead?
I figure this means what it does for cars - people who care about the details, from top to bottom, of their ride. GURPS does provide a lot of tools for what's under the hood. Much (although not nearly all) of the system has a set of quantifiable underpinnings you can use to ensure what's in play is consistent with the rest of the system.
But you don't really need to interact with that very much, if at all. Someone does - and that was true in earlier editions of GURPS and with pretty much every other game I played (check my author page for some of them). At some point, someone had to sit down and decide how things work. GURPS provides a lot of worked examples, but also a toolkit to make more if you really want more stuff and want to ensure it's consistent with the rest.
There is the "GURPS requires a lot of math" meme, which I think is connected. It does require more than some games. It requires less than others. Most of the math you do use is addition and subtraction, with some occasional multiplication - although that's usually just a table lookup (Basic Lift, say).
GURPS does require a lot of front-loaded decision making for characters - and a point budget means you have to do some basic arithmetic. But take it as someone who didn't do well in algebra and who didn't take calculus, it's simple and straightforward math. I can do it, and I only use a calculator because I've been known to make mistakes when I don't. Once play starts, you don't really need to do much except occasionally add figures, or subtract hit points, or multiply an effect by x2 or x1.5. I suppose that can be seen an onerous, but "save for half damage" doesn't make D&D for mathematicians, either.
I have to admit I'm flummoxed by the "4e is more for gearheads than 3e" idea, too. It's pretty much the opposite. While 4e does give you more toolkits to use (GURPS Powers or the technique design system in GURPS Martial Arts) 3e had them, but buried, shunted off to the side, done with a mixed bag of worked out consistent design and wild ass guesses that stuck through the system. 4e cleaned a lot of the weird exceptions and "this works like this, except for this, and unlike that" problems that crufted their way into 3e over the years. It equally streamlined a lot of the oddbad edge case decisions you'd need to make as a GM and as a player in 1e-3e, and cut it down to much simpler and more consistent choices.
Not rules-light, because even very light GURPS games have a fair set of rules you'll want to use. Not rules-heavy, because that implies that you must use a very large preponderance of rules from the books in order to make it work.
Personally, I like a system that provides a wide variety of rules for a wide variety of circumstances. GURPS does this. But so does D&D and its variant flavors - there is a system, sub-system, or variant system for everything from classes and XP gain to combat (OD&D came with multiple combat systems) to spell casting. GURPS has them, but it's a toolkit.
And don't mistake the detail-crazed noodling on the SJG Forums with how we all play. It's where people who want to explore ideas in pedantic, extreme detail do so, but it's not the whole (or even a large part) of GURPSdom. And don't mistake super drilled-down detail meant for people who specifically want super drilled-down detail as the basis for the entire system. Judging GURPS by the is kind of silly, because it's optional stuff that just happens to be 100% compatible if you choose to use it. It's easy to look at rules like "A Matter of Inches" or books like Tactical Shooting and think, this is for detail freaks. But that's just there for folks who want or need that detail - and who might equally drill down to the nitty-gritty for gun combat or sword fights but handwave social interaction (or vice-versa.)
I do get that some people really feel like a book of additional rules corrupts the game in a way to make the basic game bad - the whole "splatbooks killed AD&D 2e" thing, or AD&D being killed by Unearthed Arcana. But it seems to me that all systems have a huge variety of options, and you've always had to pick and choose what you use. Access to a lot of options seems more feature than bug.
I won't spend a lot of words here, but I want to draw attention to the false idea that GURPS is for simulationists and has no support for dramatic play.
GURPS in 4e has put in a lot more emphasis on being able to have dramatic play, for folks who like that sort of thing. Just like the "gearheady" stuff I mentioned above, it's optional. You don't need to use it, it's just 100% compatible with the rest of the system if you do choose to use it.
A good example is buying successes in play - Monster Hunters introduced the idea of Wildcard skills (big, group skills like Knight! or Magic! that cover large areas of related skills) giving points you could spend to influence events. Impulse Buys extends the idea of purchased successes. Dramatic play gets nod right there - you can do cool stuff because the scene and the character are right, not something that depends on dice. Pretty much, heroes get to be heroic just because, or crises happen because it's the right dramatic moment. GURPS explicitly supports that.
So, it's for everyone?
No, of course not. No game is. Not everyone wants what GURPS offers. But it's a big disservice to the game system to peg it as for math-loving gearheads, and thus the fans as that kind of fan. It's a different sort of toolkit than other games are, but it's not one that is solely for people who want to tinker under the hood. The worked examples (such as DF) play straight up, no tinkering or mucking around under the hood. You don't even need to care about why X costs Y points or why Power A does B . . . but you can rest assured if you want to find out there is a sensible and defensible reason why.
And in my case, with GURPS 4e, I ended up with a larger amount of my gamer friends willing to play - even those who'd disliked 3e. They found 4e more accessible. Less fiddly rules and odd special cases to cover cracks exposed in decades of play. Easier concepts to get your head around, too. I've found it easier to explain, easier to run, and require a lot less defending rules in play than a lot of other games I've played.
But that could just be me.
Doug Cole's excellent interview of Sean Punch, where he talks about some of the same ideas.