The plan with GURPS was to make it a Generic, Universal Roleplaying System, like the title says. That is, you could play any character you wanted, any genre you wanted. A great idea, to be honest. Some of my players hate learning new game systems. I kind of like it, but am liking it less and less as time goes on; I would rather take the good parts of systems I liked and tack them onto another system, because I am really tired of trying to figure out what is "balanced" in a given system, what will challenge my players without fudging. So, like I said, good idea in principle to make one genre-less system.
But the problem with picking just one system is that a game system does, to some extent, govern your style of play. If you play a highly detailed game like the Hero System, no matter how rollicking the game is supposed to be, there is a certain level of grittiness and realism that you'll see, in contrast to a game like Marvel Super Heroes, which has relatively few rules and restrictions and relies much more heavily on a GM's ability to improvise results and interpret a few die rolls as he or she sees fit. A Marvel-esque game isn't going to be as gritty, typically; it'll gloss over the details a little more, because they aren't worked into the game system.
GURPS is, if anything, more detailed than Hero. Combat turns are one second each, for instance. That means that as the GM goes around the table once to ask the PCs what they do, you'll get responses like "Go from lying down to kneeling" "Draw my gun" "Take three steps" and so forth. This just isn't my style; I prefer to hear things like "I draw my sword, grab the magic potion and dive over behind the bar." This would take about four turns in GURPS. Where's the heroism? Where's the action and excitement?
Creating characters in GURPS is fun for me; like Hero, character creation is detailed, making for characters who are more believable and realistic than their counterparts in many other systems. GURPS does seem to be somewhat easier to abuse than Hero, but then, Hero is an older game system.
Now, as I was saying, the source material that is published for GURPS is typically the highest quality in the field, or close to it. Steve Jackson, unlike White Wolf, for instance, knows how to write a sourcebook with quality material rather than moody, slipshod filler. FASA, GDW and TSR (the third to a lesser extent than the others) are the only other game companies I know of with such consistently high production values. I own two GURPS sourcebooks, Space and Imperial Rome, and both of them have almost no space wasted, no useless info. And I trust Imperial Rome to have no invented history, no lies or made-up facts.
Overall, then, GURPS isn't a game I expect to play often in the future, but it is an excellent repository for good source material which can be easily converted to other systems.